N BSTRCT OF THE ThESIS OF
in David 3. Byrne for the decree ofMaster of Science
Geoloay oreserited on November 8.1S8 Title:Stratigraphy and DepositiorialHistory cf the Ucer Mississippian Big Snowy Formationin the Srowcrest
Range. southwestern Montana. Redacted for privacy bstract approved Prof. Kjith F. Oles
The Big Snowy Formation inthe Snowcrest Rangereflects in an middle Meramecian throughlate Chesteriari deposition intermittently si lied trough insouthwestern Montana.The name by the Kibbey Big Snowy Formation hasrecently been supplanted Formation and Lombard Limestone,which compose the lower two-thirds of the SnowcrestRange Group (new). The Kibbey is poorly exposed throughout theSnowcrest Range, but canbe in the subdivided into two informalunits based on measurements Blacktail Mountains, just northof the study area.The lower unit consists predominantly ofsilty and sandy dolostoneswhich represent deposition in an upperintertidal to lowersupratidal quartz arenites, environment.Calcite- and dolomite-cemented deposited on a lower shorefaceto lower intertidalenvironment, civerlies the compose the upper unit. The Kibbey unconforrnably the Mission Canyon Limestone arid isconformably averlairi by
Lombard Limestone. Lombard carbonate sedimentationdenotes rapid basin shc'reface to the subsidence and consequentmigration of the Ribbey east in late tleramecian time. Four lithofacies are recognized in
the Lombard, whichare, in ascending order of predominant
stratigraphic occurrence,(1) lime mudstone,(2) fossiliferous
wackestone-packstone,(3) calcareous shale, and (4) dolomiticlime
inudetone lithofacies. The first two lithofacies displayan
intertonquing relationship recordingepisodic differential subsidence
in the trough. Rapid basinwide subsidence and consequent
deposition In a stratified watercolumn are reflected in the last two
1 ithofacies.
Seven major Late Mississippiantectono-sedimentary events are
suggested by regional relationshipsof the Lombard lithofacies in
the study area and correlativeunits in east-central Idaho and
central Montana. Times of uplift or cessation of subsidenceon the
outer cratonic platformseem to correlate to times of increased
subsidence on the inner cratonicplatform, and vice versa. Lombard
sedimentation responded to the combinedinfluences of episodic
subsidence within the trough and to twoperiods of carbonate bank
development on the outer cratonicplatform. The lower part of the
Lombard is dominated by the limemudstone lithofacies, which was deposited in a slightly silled basinbehind the Scott Peak carbonate bank complex.
Drowning of the bank in earlyChesterlan time corresponds with a major progradational eventdocumented in the upper part of the
Lombard. Upbuilding of the Surrett Canyonbank in late Chesterian time occurred concomitantlywith rapid subsidence of the Snowcrest trough, creating a deep, silled,vertically stratified basin characterized by calcareous shaledeposits. Subsequent shoaling of the trough is recorded in the dolomitic lime mudstone lithofacies, which disconformably underlies the overstepping Conover Ranch
Formation in the study area.
Geochemical analyses of the lime mudstone and calcareous shale lithofacies of the Lombard indicate a moderate to good petroleum source rock potential. STRATIGRAPHY AND DEPOSITIONAL. HISTORY OF THE UPPER MISSISSIPPIAN BIG SNOWY FORMATION IN THE SNOWCREST RANGE, SOUTHWESTERN MONTANA
by
David Jerome Byrne
A THESIS
submitted to
Oregon State University
in partial fulfillment of the requirements for the degree of
Master of Science
Completed November 8, 1985
Commencement June 8,1986 APPROVED:
Redacted for privacy Professor Geology in e of major
Redacted for privacy
of Depart ment /f eo logy
Redacted for privacy
Dean of Grad&i4e School
Date thesis is presented November 8,1985 ACKNOWLEDGEMENTS
To Dr. Keith F. Oles goes my appreciation for his critical review of this manuscript and for the many helpful suggestions made during his visit to the field area and during the past year. I am especially grateful to Dr. Tom 3. DeVries for hisinnumerable technical comments and criticisms, and for the many hours spent discussing the "final model" and reviewing this manuscript. I also wish to thank Dr. J.6. Johnson for his technical assistance and for reviewing this manuscript.
To my colleague, Cohn Key,I wish to extend a very special thanks for his friendship, support, and suggestions during the field investigation and subsequent preparation of this thesis.
I am indebted to U. J. Sando and 3. T. Dutro, Jr., of the
U. S. Geological Survey, for their identification of the Mississippian corals and brachiopods collected in the thesis area, and for the constant encouragement extended to the author throughout this study. Additional appreciation for their helpful technical comments and advice goes to: Jack Cox, James Ruff in, and Pat M6raw
(Tenneco Oil Company); Chip Goodhue and Dr. Alan R. Niem
(Oregon State University); Pete Isaacson (University of Idaho);
3. K. Rigby (Brigham Young University); Chris Schmidt (Western
Michigan University); and E. K. Maughan, Russ Tysdal, and Bruce
Wardlaw (U.S. Geological Survey).
A special acknowledgement goes to ray family; to ray fellow graduate students, especially Phil Rarey, Irene Jepsen, and John
Chesley; and to my special friends, Linda Blythe, Patti VanDeCoevering, Gayin Nordman, and Clay Penhollow, whose unending support, love, and encouragement will always be remembered.
The financial support provided by Tenneco Oil Company and
Shell Oil Company is gratefully acknowledged. TABLE OF CONTENTS
Page INTRODUCTION 1 Location 1 Purpose of study 1 Accessibility 3 Geomorphology and climate 5 Investigative methods 9 Geological setting 13 Snowcrest Range setting 18
PREVIOUS INVESTIGATIONS 22 Introduction 22 Historical development of nomenclature 22 The Quadrant Quartzite and Formation 22 Introduction of the Big Snowy Group 26 The Charles Formation conflict 30 The Mississippian-Pennsylvanian boundary problem 31 Relationship of the Big Snowy Formation to the underlying Mission Canyon Limestone 33 Big Snowy trough 35 Kibbey Formation 35 Otter Formation 36 Heath Formation 37 Snowcrest trough 40 New terminology 42 Kibbey Formation (revised) and Lombard Limestone 42 Conover Ranch Formation 43 Railroad Canyon Formation 43 Relationship of the Big Snowy Formation to the overlying Amsden Formation 44
RELATIONSHIP OF THE KIBBEY FORMATION TO THE UNDERLYING MISSION CANYON LIMESTONE 46 Description 46 Interpretation 57
KIBBEY FORMATION 64 Introduction 64 Description 64 Snowerest Range 64 Blacktail Mountains 72 Dolostone Lithofacies 74 Sandstone lithofacies 76 Deposit ional environment 82 Introduction 82 Dolostone lithofacies 84 Sandstone 1 ithofacies 90 Age and Stratigraphic interpretation 98 TABLE OF CONTENTS (Continued) Pao
LOMBARD LIMESTONE: DESCRIPTION 107 Introduction 107 Lime mudstone lithofacies 110 Tongue ID 119 Tongue lID 121 Tongue hID 122 Tongue IVD 122 Tongue VD and VID 123 Fossi 1 iferous wackestone-packstone lithofacies 124 Tongue IS 128 Tongue 118 130 Tongue IllS 132 Tongues IVS-VIS: Introduction 138 Tongues IVS-VIS: Lower part 139 Tongue IVS 145 Tongues IVS-VIS: Upper part 147 Tongues IVS-VIS: Uppermost part 161 Tongue VS 166 Tongue VhS 167 Clover Meadow section 172 Summary 179 Calcareous shale lithofacies 181 Dolomitic lime muditone lithofacies 192 Unit 1 192 Unit 2: Lower part 195 Unit 2: Upper part 198 Unit 3 200 Unit 4 202
LOMBARD LIMESTONE: DEPOSITIONAL ENVIRONMENT 208 Introduction 208 Lime mudstone lithofacies 208 Fosi 1 iferous wackestone-packst one lithofacies 213 Calcareous shale and dolomitic lime mudstone lithofacies 216
AGE OF THE LOMBARD LIMESTONE 221
RELATIONSHIP OF THE LOMBARD LIMESTONE TO THE OVERLYING CONOVER RANCH FORMATION 230
LOMBARD LIMESTONE DEPOSITIONAL MODEL 235 Early late to late Meramecian 235 Early to middle late Chesterian 244 Middle late Chesterian 248 Latest late Chesterian 256 TABLE OF CONTENTS (Continued) PaQe
PETROLEUM POTENTIAL 257
CONCLUSIONS 272
BIBLIOGRAPHY 277
APPENDICES 288
A: MEASURED SECTION DESCRIPTIONS 288 I. Red Reck River section 290 II. Clover Divide section 309 III. Sawtooth Mountain section 324 IV. Sunset Peak section 338 V. Hoqback Mountain section 343 VIA. Sliderock Mountain section I 361 VIB. Sliderock Mountain section II 373 VII. Snoworest Mountain section 378 VIII. Clover Meadow section 401 IX. Sheep Creek Canyon section 406
B: SOURCESFOR KIBBEY FORMATION AND LOMBARD LIMESTONE ISOPACH DATA 409
C: COLLECTION LOCATIONS OF SURFACE SAMPLES FOR GEOCHEMICAL ANALYSES (PETROLEUM SOURCE ROCK POTENTIAL) 410
D: GAS CHROMATOGRAPHY RESULTS 411 LIST OF FIGURES
Figure Page
1 Location map of southwestern Montana and adjacent Idaho, showing mountains and specific locations mentioned in text. 2
2 Map of Snowcrest Range area, showing major peaks, access routes, and measured section localities (numbers correspond with general locations of measured sections listed in Appendix A). 4
3 View of Snowcrest Range, showing hogbacks which define the ridgeline. 6
4 View of typical geomorphic expression of upper Paleozoic units in Snowcrest Range, showing characteristic valley between two ridges or hills composed of Madison Group (Mine) carbonates and Quadrant Formation (M Pq) sandstones. 8
Recent landslide deposits involving failure within the Big Snowy Formation, on western flank of northern Snowcrest Range. 10
6 Mississippian paleotectonic elements in the western United States. 14
7 Isopach map of Late Mississippian rocks of southwestern Montana. 17
8 Geologic map of southwestern Montana. 20
9 Nomenclature, faunal zonat ion, and temporal relationships of Upper Mississippian and lower Pennsylvanian units in southwestern and west central Montana. 23
10 Diagrammatic north-south cross section showing spatial relationships of Carboniferous age rocks in Montana as interpreted by Scott (1935). 28
11 Schematic cross section across the Big Snowy trough, showing gross facies relationships and diachronic nature of the Big Snowy Group formations. 39
12 Solution collapse breccia at Clover Divide. 56 FiDure PaDe
13 Photograph of isolated Kibbey Formation outcrop at Sawtooth Mountain. 66
14 Bimodal sorting in quartz arenite of Kibbey Formation. 68
15 Kibbey Formation section in Blacktail Mountains. 73
16 Dolomitized bioclast (echinoid plate or ossicle fragment?) in dolomitic quartz arenite. 79
17 Plane laminated quartz arenite. 81
18 Isopach Map of the Kibbey Formation in southwestern Montana. 101
19 Isopach Map of the Kibbey Formation in the Late Mississippian Snowcrest trough. 102
20 Map illustrating Lombard Limestone to Kibbey Formation thickness ratios in the Late Mississippian Snowcrest trough. 106
21 Typical sparse biomicrite of lime mudstone lithofacies. 114
22 Silty fossiliferous micrite in lime mudetone lithofacies. 120
23 Photomicrograph of poorly washed echinoidal biomicrite. 127
24 Photomicrograph of echinoid-bryozoan biosparite (grainstone) at the base of tongue 1115 (unit 41), Snowerest Mountain section. 134
25 Representative specimen of the tabulate coral Michelinia cf. rneekana which occurs throughout fossiliferous wackest one- packstone tongues IZIS-VIS. 136
26 Photomicrograph of poorly washed biopelmicrite. 141
27 Photomicrograph of foraminiferal biomicrite in tongue IVS. 143
28 Photomicroqraph of bryozoan biomicrite. 149 Figure Page
29 Specimen of Vesiculophyllum sp. from unit 11 at Siderock Mountain II section. 151
30 Brachiopods collected in upper part of Lombard Limestone at Sliderock Mountain (units 10 and 11, section II). 152
31 Photomicrograph of wood(?) fragment in silty biomicrite. 154
32 Solitary rugose coral (Siphonophvllia sp.) from the upper part of Lombard Limestone (unit 50, Sawtooth Mountain section). 138
33 Brachiopods collected in units 13, 22, and 50, Lombard Limestone, Sawtooth Mountain section. 159
34 Photomicrograph of sorted biosparite. 162
35 Limestone lithoclast conglomerate exposed at base of dip slpoe on hill (9,566') just west of Sawtooth Mountain (unit 53; U 1/4, SW 1/4, section 8,T.12 S., R. SW.) 164
36 Photomicrograph of finer fraction of limestone lithoclast conglomerate. 165
37 Photomicrograph of packed biomicrite. 170
38 Encrusting bryozoan on partially silicified impunctate brachiopod valve. 171
39 Lombard Limestone exposed in west-facing upper cliffs at Clover Meadow, north-central Gravelly Range (SW 1/4, NE 1/4, section 16, T. 9 5.,R. 2 U.). 173
40 Two specimens of Sighonophyllia sp. collected from Lombard Limestone in lower cliff sequence (unit 41) at Clover Meadow, north-central Gravelly Range. 175
41 Lombard Limestone exposed in lower cliffs at Clover Meadow, north-central Gravelly Range (SW 1/4, NE 1/4, section 16, T. 9 S., R. 2 U.). 176 Figure PaQe
42 Calcareous shale outcrop in large gully at base of dip slope of hill (9,566') west of Sawtooth Mountain (14 1/2, SW 1/4, section 8, 1.12 S.,R. S 14.). 182
43 Photomicrograph of calcareous shale (silty spicular miarit&. 185
44 Photomicrograph of phosphatic interval of calcareous shale lithofacies at Sawtooth Mountain. 188
45 Dolomitic lime mudstone lithofacies exposed in northwest-facing cliffs on northwest flank of Sawtooth Mountain (NW 1/4, SE 1/4, NE 1/4. section 9,1. 12 S., R. 5 14.). 193
46 Photomicrograph of mottling in dolomitic lime mudstone. 197
47 Photomicrograph of uppermost color-mottled dolomitic lime mudstone unit (unit 59) at Sawtooth Mountain. 204
48 Close-up view (photomicrograph of transition between gray and orange mottles. 206
49 Time stratigraphic chart showing temporal relationships of Late Mississippian units in east central Idaho, southwestern Montana, and central Montana. 222
50 Lombard Limestone-Conover Ranch Formation transition exposed in cliff exposure at Sawtooth Mountain NW 1/4, SE 1/4, NE 1/4, section 9, 1. 12 S., R. 5 14.). 231
51 Close-up view of Lombard Lirnestone-Conover Ranch Formation contact. 233
52 Isopach map of Lombard Limestone in southwestern Montana. 242
53 Isopach map of Lombard Limestone in the Late Mississippian Snowcrest trough. 243
54 Map of southwesternmost Montana showing abandoned well locations and surface sample collection locations for source rock analyses. 258 Figure Page
55 Generalized tectonic map of southwesternmost Montana showing position of inferred sub-Snowcrest Range thrust fault and relationship with Tendoy and Medicine Lodge thrust sheets (from Perry et al, 1983). 260
56 Hypothetical cross section (B-B') through Snowcrest Terrane (from Perry et al, 1983). 261
57 List of standards for petroleum source rock analyses used in this report (used with permission of Tenneco Oil Company). 265
58 Classification of source rock kerogen types based on hydrogen and oxygen indices. 269
59 Evaluation of genetic potential of selected samples from the Lombard Limestone. 271
60 Terminology for thickness of beds and laminations, for splitting and parting habit of units within beds, and for bedding-lamination terminology (modified from Collinson and Thompson, 1982). 289 LIST OF TPBLES
Table Page 1 Textural and faunal characteristics of lime mudstone and fossiliferous wackestone- packstone lithofacies 180
2 Ligt of fossils recovered in study area 225
3 Data obtained from source rock evaluation of Lombard Limestone samples 263
4 Results of Rock-eval pyrolysis on Lombard Limestone samples 264 LIST OF PLATES
Plate 1 Historical development of Late Mississippian and Pennsylvanian nomenclature in southwestern and central Montana pocket
2 Columnar sections of the Kibbey Formation in southwestern Montana pocket
3 Stratigraphic relationships of Lombard Limestone lithofacies in southwestern Montana pocket
4 Schematic representation of Late Mississippian deposition in southwestern Montana pocket STRATIGRAPHY AND DEPOSITIONAL HISTORY OF THE UPPER MISSISSIPPIAN BIG SNOWY FORMATION IN THE SNOWCREST RANGE, SOUTHWESTERN MONTANA
INTRODUCTI ON
Location
The Snowcrest Range is located in southeastern Beaverhead arid
southwestern Madison Counties, approximately 33 miles southeast of
Dillon, Montana. The range, which rises abruptly above the gentle,
low-relief hills and valleys which surround it, describes a northeast to southwest arc (Fig.1), and is overthrust and overturned to the
southeast. The area under study encompasses approximately 440 square miles and incorporates nine U.S. Geological Survey 7.5 minute quadrangles, which, from southwest to northeast, are the
Lima, Henry Gulch, Lima Dam, Whiskey Springs, Antone Peak,
Swamp Creek, Stonehouse Mountain, Spur Mountain, and Home Park quadrangles. The Snowcrest region, as defined here, lies between
44°40' and 45002, north latitude, and 11l°58' and 112°30' west
longitude (Fig. 1).
Purpose of Study
The principal goals of this study are:(1) to measure and construct several detailed stratigraphic sections through the Upper
Mississippian Big Snowy Group rocks exposed along the length of the Snowcrest Range;(2) to subdivide the Big Snowy Formation into members or lithofacies;(3) to determine the Late Mississippian deposit ional environments in the Snowcrest Range area;(4) to correlate these rocks to regionally equivalent units;(5) to provide 10 mx 1C-.i IDD01 0.-1cfl C) --z z0 0.00-.o z z*i I, 1w 3 0 '- r .)s'3'z' ' z 0Iam-I iiD 3 Ia3 V) 0.C 0 i £33rt ID . I, 3hillAc 0.--sDW.D .l -. m ai -h0 I_D 0. .-. ID ID -tIm bOIIISi%m.4ô4) P -4 1*ito -. 0-. d 1 '4 - y:iNo EIiQIOAN r.3 0 I.00o'-'1 i ittP5 I-. V\4 ( 0.0ID3a, . ii 3 0.a, N FI 's" J'Ia '.r 2 d0 3 4-. oo. ID 0 f! I 313d-ID .-' 3 NATIONALYELLOWSTONE PARK 0 I 3
evidence for deposition in an unstable, subsiding trough; and,(6) to
analyze the hydrocarbon source-rock potential of the Upper
Mississippian rocks in the Snowcrest Range area. Very little
detailed work has been accomplished in the Snowcrest Range. To
my knowledge, no one has undertaken a stratigraphic analysis of
the Big Snowy Formation involving detailed petrographic,
biostratigraphic, or geochemical analyses. This paucity of
investigation probdbly can be attributed to the inaccessibility of the
heart of the range where the upper Paleozoic rocks are best
exposed. Previous reconnaissance work did reveal an exceptionally
thick Carboniferous sequence here, meriting a detailed investigation of these rocks (Kiepper, 1950; Sealy, 1953). The location of the
Snowcrest Range, with respect to the inferred geometry of the
Snowcrest trough, affords an unsurpassed opportunity to study Big
Snowy deposition in an axial part of the Snowcrest trough.
This report concentrates on the late Meramec and Chester age
Big Snowy Formation. complementary report on the latest
Chester and Pennsylvanian Amsden Formation and lower part of the
Quadrant Formation is concurrently being prepared by Cohn Key, also of Oregon State University.
fccessibi I ity
Three gravel and dirt roads, which follow the major valleys, permit access into the Snowcrest Range area (Fig. 2). The southwestern end of the range can be reached along either the
Centennial Divide or Blacktail Deer Creek roads. The Centennial
Divide road continues north along the easternrnost flank of the _L4r / ( I NTN. USeufSd ...II.. LEGEND # I It ! 0 NEIp 'I. - M.I.tSSSNda'p StgNwsy . Nu.rvSII IX ,' ., . . _ : 0 £ Nil., psal P.,.,.P,I.ItIv. a...... e Riabt C:::: 5 :' VU Siovis VIII 0 I IISNOCMTN vi £ £osoi II, t iii&?.tXlO0TII lv 0 MONTANA DELL p sr' rçY 1O550 $ Iu.i.I., N 0 .lhu4 N Figure 2. Map of Sr.owcrest Range area, showing major peaks, LIN access routes, and NIL.. sectionsmeasured sectionlisted inlocalities Appendix (r,umbersA). Rivers arId streams not shown. correspond with general locations of measured - 5
Snowcrest Range and eventually joins with the Ruby River road
north of Lone Butte. The northeastern end of the range is best
approached from the town of Alder, Montana, via the Ruby River
road. This road is generally well maintained throughout the
summer months and can be travelled during and after inclement
weather with few problems. Centennial Divide and Blacktail Deer
Creek Roads can present difficult driving conditions, however, and are often impassable immediately following heavy rains. Access
into the range is usually best during July, August, and early
September.
Several secondary dirt roads provide access to the western part of the range, the most notable including the Antone Peak
(Forest Route 32), East Fork Blacktail Deer Creek (Forest Route
963), Ledford Creek (Forest Route 833), and Robb Creek roads.
Most of the secondary roads are impassable to two-wheel drive vehicles during much of the summer because of mud from daily thundershowers, or from gully erosion which incises the roads.
Access to the interior of the Snowcrest Range is restricted to foot, horseback, or helicopter.
Geomorpholoqy And Climate
The Snowcrest Range is a succession of hogbacks which rise gradually in elevation from low, rolling hills at the southwestern end to narrow, precipitous ridges in the central and northern parts of the range (Fig. 3). Resistant Carboniferous and Permian rocks form the backbone of the range throughout the 40 mile length.
The principal crest of the range attains a maximum elevation of r1
Figure 3. View of the Snowcrest Range, showing hogbacks which define the ridge line. Three highest peaks, from right to left,are Sunset and Olsen Peaks, and Hogback Mountain. View is to the north from Sawtooth Mountain. 7
10,605 feet at Hogback Mountain; to the north the major peaks
maintain summit elevations in excess of 9,000 feet. The central
part of the range, where a th maximum relief of approximately
4,900 feet is attained, is characterized by six peaks which exceed
10,000 feet in elevation.
characteristic ridge-valley-ridge geomorphological expression
is ubiquitous in the Snowcrest Range wherever the Mission Canyon
Limestone, Big Snowy, Pmsden, and Quadrant Formations are all
present. The Quadrant typically caps the highest peaks and ridges
in the range, except where the Permian Phosphoria Formation
overlies the Quadrant on the normal-up limb of the overturned
anticline. Each Quadrant-supported ridge is typically paralleled by
a subordinate ridge of Mission Canyon limestones and dolomites.
These two ridges are separated by the less resistant valley- and
saddle-forming Big Snowy andmsden Formation rocks (Figs. 3 and
4). Pt several locations where the Mission Canyon is missing
because of thrust faulting, the Big Snowy rocks form a subordinate ridge or hill adjacent to the Quadrant ridges which is best displayed at Sawtooth and Hogback Mountains. The Pmsden
Formation is the least resistant of the four units in the range.
The linear continuity of the Snowcrest Range is broken by three drainage systems which dissect the ridge line and divide the range into four distinct sections. These four drainage systems, from southwest to northeast, are Blacktail Deer, Robb, and Ledford
Creeks (Fig. 2) The natural structural extension of the range to the north-northeast is the Greenhorn Range. It is separated from the Snowcrest Range by the antecedent Ruby River which flows 13 F:'
Figure 4. View of typical geomorphologic expression of upper Paleozoic units, showing characteristic valley between two ridges or hills composed of Madison Group (Mmc) carbonates and Quadrant Formation( fPq) sandstones. Photo in southwesternmost part cf the range, looking north (MbsBig Snowy, MfPa=msden). miles northward from its origin on the southeastern flank of the central Snowcrest Range before abruptly swinging northwest through the watergap between the two ranges.
Gently sloping erosional benches, cut into overturned and normal-up Mesozoic and Tertiary units, skirt the Snowcrest Range on both the northwest and southeast sides. The rugged nature of the range was enhanced in Wisconsin time when glaciers carved cirques and small valleys in the higher parts of the range. Failure of the overturned, northwestward-dipping Big Snowy Formation has resulted in the development of large, recent landslides near Spur and Snowcrest Mointains (Fig. 5).
The climate of southwestern Montana is semi-arid as a result of its interior position immediately east of the continental divide.
Annual precipitation averages 15 inches, and is greatest from April through July. Summer temperatures range from lows in the upper thirties at night, to highs near 1ø°F during the day. During the summer the Snowcrest Range is characterized by afternoon thunderstorms which sweep over the range on a near-daily basis.
Investigative Methods
Field work was accomplished over a ten week period, from
June 27 to September 1,1985. Seven stratigraphic sections were measured at nearly equal spacings along the length of the
Snowcrest Range, as well as one section each in the Blacktail and
Gravelly Ranges (Fig. 2). A total of 10,920 feet of section were measured and described. 10
Figure 5. Recent landslide deposits involving failure within the Big Snowy Formation, on western flank of northern Snowcrest Range. View is to southwest from Snowcrest Mountain area. Sliderock arid Spur Mountains in distance. 11
adequate exposures of the Big Snowy Formation, permitting detailed stratigraphic analysis, are largely limited to the high peaks
in the Snowcrest Range, and the northeastern flank of the Blacktail
Range. The partial Big Snowy Formation section measured in the northern part of the Gravelly Range has not been reported before, and this is the first reported occurrence of Big Snowy rocks east of the Greenhorn Fault, which defines the southeastern edge of the
Snowcrest and Greenhorn Ranges. Previous workers had assigned these rocks to the Mission Canyon Limestone (Hadley et al., 1980).
Individual field stations were recorded daily in a notebook and pertinent structural data and formation contacts were transferred onto U. S. Geological Survey 7.5 minute topographic maps having a scale of 1:24,000. Stratigraphic thicknesses were measured using a
Jacob's 'staff and Abney level, or with a metal tape with subsequent adjustments for bedding attitudes. Individual bed thicknesses were measured in the field with a metal tape; the terminology used for stratification and splitting properties is based on standards established by Mckee and Weir (1953). Bedding attitudes were measured with a Brunton compass.
Sandstones were classified according to Williams, Turner, and
Gilbert (1954). reference sand grain gauge was utilized in the field for determining sand grain size (after Wentworth, 1922) arid roundness (after Powers, 1953). Carbonate rocks were classified in the field according to Dunham (1962), and additionally classified according to Folk's (1962) terminology in the laboratory. The degree of crystallinity of the carbonate rocks was recorded relative to the Wentworth scale for clastic rocks (Wentworth, 1922); fine, 12
medium, and coarsely crystalline carbonates are directly analagous
to fine, medium, and coarse sand-size fractions. The Geological
Society of America Rock-Color Chart (Goddard et al., 197) was
used to determine rock colors on both fresh and weathered
surfaces. Dolomite was contrasted with calcite in the field by
comparing the rate of effervescense upon application of hydrochloric acid to a fresh rock surface. The dolomite typically
yielded a slower and less energetic reaction.
For lithological and/or paleontological analysis, 3ø rock samples were collected in the field. Each sample taken for
lithological study was removed directly fromoutcrop; float samples were not utilized. However, a small number of fossil collections were made from float, but only where the beds which were the source were obvious. An additional 22 samples were taken for geochemical analysis, to determine hydrocarbon source rock potential. Only the freshest surface samples obtainable were collected from promising intervals; generally, samples could not be broken out beyond one to two feet deep into the outcrop. These samples were immediately wrapped, unmarked, in several layers of aluminum foil and labeled externally. Direct handling of each sample was kept to a minimum.
All of the samples collected for lithological analysis were cut and polished for inspection under a binocular dissecting microscope;
180 samples were then selected for thin section analysis.The presence of dolomite was determined by petrographic analysis (using
Alizarin Red stain), and X-ray diffraction techniques.
A total of 72 coral and bryozoan samples, and 46 brachiopod 13 samples, were identified and zoned by Dr. W.J. Sando and
Dr. S.T. Dutro, respectively, both of the U. S. Geological Survey in
Washington, D.C. additional analysis of paleoritalogical material was facilitated by Dr. S.S. Johnson, Bob Blodgett, and Ning Zhang, all of Oregon State University.
Rocks collected for geochemical analysis were sent to Tenneco
Laboratories in Houston, Texas. Geochemical analyses to determine hydrocarbon source rock potential included total organic carbon, kerogen content, soluble organic matter, spore color indexing, and vitrinjte reflectance. Of these samples, Rock-Eval Pyrolysis and gas chromatography tests were completed on eight samples which displayed indices supporting a fair to good source rock potential.
Geological Setting
The Montana-Wyoming-Idaho tn-state region occupied a position on the westernmost edge of the stable North merican craton throughout Mississippian time. This part of the craton, known as the Cordilleran platform, was bordered on the northeast by the Canadian shield, and on the east by the Transcontinental arch, a linear, northeast-trending positive element which extended from southern Manitoba to northern Mexico. To the west, the platform was bordered by the Cordilleran geosynclinal belt. Within this belt, three tectonic elements can be discerned: the western
Cordilleran eugeosyncline, the eastern Cordilleran miogeosyncline, and the intervening positive Antler orogenic belt (Fig. 6; Sando,
Gordon, and Dutro, 19Th).
Most of Montana, Wyoming, and western North and South CANADIAN r - SHIELD
Ui oI Ui
z, SNOWY...WILIiScON if
BASLJ- JLj WYOMING )COP9SLLERAN BASIN j0 / PLIATFORM C-)---- - / c
UINTA'f I
Figure 6. Mississippian paleotectonic elements in the western United States (compiled from Sissler (1976), Sando (1976), Smith and Gilmour (1979), and Maughan (1984).
I- 15
Dakota were occupied by a broad cratonic platform during the
Paleozoic Era. Orogenic activity, related to plate collision from
latest Middle Devonian to early Mississippian time, created
instabilities in the previously more stable platform, causing
differential movement within both the platform and geosynclirial
belt (Gutschick and Sandberg, 1983; Sando, 1976). Deposition of
Mississippian strata in the northern Rocky Mountain region thus reflects the direct and indirect influence of regional orogenic activity which generated variability within the paleotectonic elements of western North America.
Three major incipient or rejuvenated areas of intracratonic instability, transverse to the craton margin, exerted significant control on Carboniferous sedimentation (Fig. 6). The northernmost of these, the Big Snowy trough in central Montana, developed in late Kinderhook time just north of the position of the early
Paleozoic central Montana trough (Peterson, 1981). This east-west-trending structural sag permitted a direct connection of the Williston basin sea, in eastern Montana, western North arid
South Dakota, and southern Saskatchewan, with the Cordilleran sea to the west.
Mississippian isopach maps indicate that considerable downwarping occurred in the trough in Osage and earliest Meramec time. Rejuvenation of downwarping, subsequent to brief epeiric uplift associated with anorogenesis, is indicated by a thick, areally restricted late Meraraec- Chester section in the Big Snowy trough
(Craig, 1972).
Tectonic activity during this latter time promoted the growth of 16
several local uplifts and new source terranes peripheral to the
subsiding basins, initiating an influx of terrigenous material into
the platform region unknown in Early Mississippian time (Sando,
1976).
The western extension of the Big Snowy trough, in southwestern Montana, is called the Snowcrest trough (Fig. 7;
Maughan and Roberts, 1967). Recently, the names Ruby and
Blacktail-Snowcrest trough have been cited as well (Peterson, 1981;
Pecora, 1981). The Big Snowy and Snowcrest troughs were separated by a northwest-trending positive element, the Lombard arch, which was located immediately north of the Bridger Range in southwestern Montana (Fig. 7). Big Snowy andmsden strata thinned over this structural high and a major facies change within the upper Big Siowy has been noted across the arch (Blake, 1959;
Harris, 1972).
The mechanisms of the instability responsible for the location of the Big Snowy and Snowcrest troughs across Montana are uncertain. These unstable troughs are coincident with a hypothesized Precambrian aulacogen which projected into the craton from a major salient of the continental margin in east-central
Idaho (Maughan, 1984). The zero thickness line of the Big Snowy
Group sediments, which is primarily fault controlled, corresponds closely with the margins of both the Big Snowy and the Snowcrest troughs. additionally, the overlyingmsden Group is less restricted areal].y than the underlying Big Snowy Group, suggesting that syndepositional and/or post-depositional (pre-fmsden) faults may have played a major role in controlling the geometry of the ALEERTA SHELF 0
.JIi4 AR Joo) C1f øI JI Is 0
j..,
\i#j AL it ' >X I - - . . - . . I,
I
U
Figure 7. Isopach map of Late Mississippianrocks of southwestern Montana. Palinspastic røstoration to account for Mesozoic and Cenozoic thrustingshown by cross-hatched pattern (modifiedfrom Peterson, 1981). trough during Big Snowy deposition (Mallory, 1972).
Subsidence of the Big Snowy-Williston, Wyoming, and Uinta
basins isolated intervening shelfareas, which also varied in
stability through Carboniferous time, locally becoming positive
elements which influenced sedimentation patterns. The northern
margin of the Big Snowy-Snowcrest trough in Mississippian time
was bordered by the relatively neutral lberta shelf (Fig. 7). The
extent of Big Snowy deposition north of the presently recognized
trough margin is unknown because of the pre-Jurassic uplift and
erosion of the southern part of the alberta shelf knownas the
Milk River uplift (Smith and Silmour, 1979).
South of the trough, the Wyoming shelf (Beartooth platform of
Peterson, 1981) seems to have varied in stability from middle
Meramec to late Chester time. Outliers of Kibbey(?) Formation
sandstones suggest an intermediate degree of tectonic stability in
early Chester time (Sartdo et al..,1975). By middle Chester time,
however, a positive peninsular element, the southernMontana arch,
had developed along the southern Montanastate line area, separating the Wyoming and Big Snowy basins until latest Chester time (Sando, 1976).
Snowcrest Range setting
Southwestern Montana is characterized by two distinctly different structural and stratigraphicfabrics which reflect the transition across the Mississippian hingeline, from the cratonic platform setting to the the miogeosynclinalsetting. This hinge line, named the Wasatch line by Kay (1951),extends from 19
northwestern Mexico to southeastern British Columbia (Fig. 6;
Stokes, 1976). The miogeosynclinal area is typified by complex,
northwest-trending, Sevier-type thrust faults and associated
asymmetric to recumbent folds (Perry and Sando, 1982). n
extremely thick sequence ofupper Paleozoic rocks is found here,
which has been tectonically thickened by structuraltelescoping.
East of this complex terrana, in the former cratonic shelf
area, major thrusts occur along the flanks of broad ant iclinoria
involving the Precambrian crystalline basement. These broad uplifts
radiate outward from a common origin in the Tobacco Root
Mountains region. In clockwise fashion, from east to west, these
major arches are the Madison-Gallatin, Madison-Gravelly,and
BlacktailSnowcrest uplifts, separated by the Madison andUpper
Ruby synclinoria, respectively (Fig. 8; Huh,1967). Upper Paleozoic
units are substantially thinner here, except inthe Snowcrest trough area, where an anomalously thick Carboniferoussequence is present
(Peterson, 1981).
The Sriowcrest Range isa southeast-verging asymmetric to overturned anticline associated with basement-involvedthrusting on the southeastern flank of the LaramideBlacktail-Snowcrest uplift.
Fault-related folding juxtposes hanging wallanticlines against footwall synclines in the central and northernparts of the range.
Uplift of the Snowcrest Range has been facilitatedby two to five miles of southeastward transportalong the southwest- northeast-trending, Late Cretaceous to early EoceneSnowcrest and
Greenhorn faults, collectively referredto as the
Snowcrest-Greenhorn thrust system (Scheedlo, 1984). The UNITk 1' TOBACCO hOOT OOI LARAUIDI UPISEDIMENTARY fl \ P ROCKS J L j/ ' O AJ 4,i M Q4 MESOZOIC ROCKS 1 i 'ç)( c._ ,' 4 ElPALEOZOICROCKS \
PC PRECAMBRIAN / (\ N BASEMENT tLt / 4 ) * !_#) 04 I'-J b PAU:: : PC
' N
N - NORMAl. I : ' / L -RUIVER11CAI. N I PC
PAIILT$ANOUNIT ;' U N cI CONTACT$DA$IIED s. \ lB' ,' WHEREINFERRED. L P '.1 // PC PC \ i f - . NTANA I
P
O S 1* r MItES :u I I
Figure 8. Geologic map of southwestern Montana. Post-Laramide sedimentary and volcanic rockshave been removed (From Scholten, 1967). 21
northwestern flank of the range is outlined by listricrange-front
normal faults which parallel the thrust faultsand are down-dropped
to the northwest. These normal faults, in addition to the
northwest-trending tear faults which dissect therange, have largely
defined the Ruby basin, a haif-graben lying northwestof the
Snoworest Range (Scheedlo, 1984).
The Snowcrest-Greenhorn lineament parallelsan earlier zone
of basement weakness along the northwesternmargin of the
Carboniferous Beartooth platform, and is believedto have played a
major role in Late Mississippian and Pennsylvaniansedimentation in
this area (Perry et al., 1983). Pre-Amsden uplift on the east side
of the Greenhorn fault removed the entiresequence of Big Snowy
rocks, yet a 600 foot thick section is presenton the west side of the fault (Hadley et al., 1980).
Uplift in the Gravelly Range (Fig.1) took place in late
Paleocene and Eocene time inresponse to regional east-west compression and consequent eastward displacementalong detachment thrusts at depth. Development of this north-trending Gravelly
Range fault zone was coincident withthe culmination of thrusting and folding along the Snoworest-Greenhornthrust system (Scheedlo,
1984).
The Blacktail Range (Fig.1), immediately north- northwest of the Snowcrest Range, ismade up of allochthonous
Paleozoic through Cretaceous stratathrust from the west (Pecora,
1981). Big Snowy exposures hereare good, but tectonic thickening and complex folding in these rocks,typical of the Overthrust belt, is prevalent throughout therange. 22
PREVIOUS INVESTIGATIONS
Introduction
Three major deposit ional packages of inner cratonic platform
origin are recognized in the Mississippian and Lower Pennsylvanian
rock record in Montana. These are, in ascending order, the
Madison, Big Snowy, and Amsden Groups.
Each group represents a major diachronic cycle separated bya
hiatus of variable duration, which is generally shortestnear the
miogeosynclinal axis (Fig. 9; Sando et al., 1975). Paleotectonic
conditions in Montana were similar throughout Mississippianand
Pennsylvanian time, although the progressive increase inclastics delivered to the Big Snowy and Snowcrest troughs is reflectedin the unique stratigraphy of each aforementionedgroup.
The historical development of Big Snowy nomenclature, spanning almost one century, has involved several changesof the upper and lower boundaries, age assignment, areal distribution, and correlation with time-equivalent units in adjacent depositional basins. The reader is referred to plate 1 to facilitatea better understanding of the development of the Big Snowynomenclature, which will be discussed first.
Historical development of nomenclature
The Quadrant Quartz ite and Formation
Carboniferous age rocks in southern Montanawere first mapped and described by Iddings and Weed (1899)during a ten year long study in the Gallatin Range (1883- 1893), where they named 23
-- soimismis uo.irm& s.sy PkIpsi I I Mma.. j It ______I a QuókMt svits P.ck.t J AI..kâBSI%OhL*.
I Tylot Fm. Ranch Iio,asIlOa ConO - %4.*IhF" 4 3 0
--
a
__I I
j5j I
I Mission Charlos Mission Canyon Llm.ston. I Canyon , -----
Figure 9. Nomenclature, faunal zonation, and temporal relationships of Upper Mississippian and Lower Pennsylvanian unitsin southwestern and west-centralMontana. Compiled from Sando and others (1975), Davis (1983), Euthrie (1984), Sandoand others (1985), and Wardlaw and Pecora(1985). 24
the Quadrant Quartzite from exposureson the southwest corner of
Quadrant Mountain (Weed, 1896). In this area the name Quadrant
was used for the strata between the underlying Lower
Carboniferous Madison Limestone and the overlying Permo-Triassic
Teton Formation (subsequently renamed the Phosphoria Formation).
Following a field conference with Iddings and Weed, prior to
publication of their type section in northwestern Yellowstone Park
(Iddings and Weed, 1899), Peale (1893) applied thename Quadrant
Formation to rocks in the Three Forksarea which he believed to
be stratigraphic equivalents to the quartziteson Quadrant
Mountain.
During field work in the Little Belt Mountains of central
Montana, Weed (1896, 1900) subdivided the Quadrant Formation into
two new formations and raised the Quadrant togroup status. The
basal formation, the Kibbey Sandstone,was named for reddish and
yellowish, argillaceous, gypsiferous sandstones resting unconformably
on the Madison Limestone. No type localitywas established, but moderate to good exposures are knownnear Kibbey School on Little
Otter Creek, and along Belt Creek, near Riceville, Montana (Weed,
1899, 1900; Easton, 1962).
Weed designated the green and gray shales intercalated with thin limestones, which conformably overlie the Kibbey,as the Otter
Formation. Both the Kibbey and Otter were assigneda
Mississippian(?) age. On the north side of the Judith River, near
Utica, he identified an overlying succession of liraestonesand sandstones below the unconformably overlying JurassicEllis Group; he left this sequence undifferentiated, but includedit in the 25
Quadrant Group (Weed, 1900).
In a later study to determine thesource beds and reservoirs
of oil accumulation in centralMontana, Freeman (1922) returned
the Quadrant to formational statusand proposed the addition of
two new members above the }(ibbeySandstone and Otter Shale.
Based on outcrops in the Big SnowyMountains, east of the Little
Belt Mountains, he introduced theTyler Sandstone, white and red
sandstones interbedded with varicoloredshales, and the overlying
Alaska Bench Limestone,a gray, fossiliferous limestone unit. A 100
foot thick gray shale, which heleft unnamed, separates the two
members.
Paleontologists of this timewere uncertain of the exact age
of the Quadrant Formation,advocating both a Mississippian and/or
Pennsylvanian age for these rocks. Because of the similarity of
fossils in the lower part of theQuadrant Formation to known
Mississippian forms, anda fauna in the upper part resembling that
of Permian rocks in Texas andOklahoma, a Permo-Carboniferous
age was suggested for the formation (Freeman,1922). Hammer and
Lloyd (1926) shortly thereafterpublished a detailed study of the
Paleozoic formations of centralMontana in which they concluded
that the upper part of theQuadrant Formation is Pennsylvanian, based on the lithologic similarityto the Pennsylvanian Tensleep
Formation in Wyoming.
Reeves (1931) argued, however,that the Quadrant Formation in central Montana is entirelyMississippian based on faunal evidence which confirmed, withone exception, a Chester age for the uppermost limestone beds. Consequently, he included all of the rocks resting between the MadisonLimestone and the Ellis Group,
in the Big Snowy Mountains, inthe Quadrant Formation. He did
not, however, subdivide the Quadrantinto the formal units
recommended by Weed (1900) and Freeman (1922) The one.
exception, a fauna identifiedas belonging to an "obscure phase of
the Chester or of the Pottsville", led Reevesto point out the
possible equivalency of the uppermostQuadrant Formation in
central Montana with the lower partof the Ameden Formation in
northern Wyoming.
Introduction of the Big Snowy Group
Scott (1935) commented on the historicallyloose application of
the Quadrant Formation to rocksranging in age from Middle
Mississippian to Permian, concluding thatthe
"...lack of knowledge of the meaning of theterm 'Quadrant' has led many geologists to consider therocks of this formation as extremely variablein nature; yet, certain thin zones of limestone and shalesare persistent under many hundred square miles in centralMontana."
t the type section in YellowstonePark, the Quadrant Quartzite was originally described as a sequence of "white,yellowish, and occasionally pink beds of quartzite withintercalated beds of drab saccharoidal limestone", underlain bya 100 foot thick talus slope
(Weed, 1896). Scott (1935) traced the Quadrant Quartzite northward from its type locality andobserved that the formation thins to a zero edge five miles northof Lombard, Montana, and that, in general, the calcareouszones become more significant west and northwest of the type locality. He also established that the
Amsden of northern Wyoming,consisting of a lower red magnesian 27
shale or sandstone member andupper limestone member, extends
northward into central Montana, thus concurringwith Reeves'
(1931) earlier hypothesis. Reeves had previously correlated the
limestone beds in the uppermost Quadrant Formation ofcentral
Montana to the lower part of the QuadrantQuartzite in northern
Wyoming.
To resolve this Quadrant Quartziteversus Quadrant Formation
conflict, Scott (1935) analyzed the regionalstratigraphic
relationships of the units lying immediatelyabove and below the
Amsden Formation to establish the trueconnection between the
Quadrant of central Montana and thatof northern Wyoming.
Through a series of southeast-tonorthwestcross sections he was
able to show two very differentlithological sequences, separated in
time and space by the laterallycontinous, though lithologically
variable, Pmsden Formation (Fig.10).
Based on recognition ofa sandstone-limestone-shale
series lying beneath the msden Formation in the Big Snowy
Mountains, a series whichwas absent in northern Wyoming, Scott
(1935) abandoned the term Quadrantin central Montana. He
replaced it with the Big Snowy Group(new) and the overlying
msden Formation. In the Big Snowy Group he included the
Kibbey and Otter Formations of Weed(1900), and introduced a new, third unit, which he named theHeath Formation (Scott, 1935). The
Heath, named for excellentexposures along the northern flank of the Big Snowies, is madeup chiefly of black, petroliferous and fossiliferous shales with three thicksandstone units which occur in the upper half of the formation. Freeman (1922) had previously NORTH SOUTH CENTRAL THREE FORKS, S MONTANA- MONTANA MONTANA N. WYOMING
AM S DEN >- QUADRANT : IHEATH 0 AMSDEN 2: U) OTTER KIBBEY MADISON MADISON
Sandstone Limestone Calcareous Sandstone
Shale bolomlte '-'- Unconformity
Figure 10. Diagrammatic north-south cross section showing spatialrelationships of Carboniferous age rocks in Montana,as interpreted by Scott (1935). 29
classified these sandstones, andinterbedded shales and thin
limestones, under the name Tyler,and had placed the underlying
shales in the Otter Formation. Scott (1935) disagreed with this
division, and lowered the top ofthe Otter to a widespread
limestone bed rich in productidbrachiopods. This corresponds well
with a relatively abrupt colorchange in the shales from vivid green
to dark gray. Thus the Tyler and upper part of the Otterwere
supplanted by the Heath Formation.
All three formations in the BigSnowy Group were assigned a
Chester age based on faunalevidence and stratigraphic position, the
Heath being consideredas "no older than Warsaw and no younger
than upper Chester" (Scott,1935). The Amsden Formation was
presumed to be conformable withthe underlying Heath Formation
and, believing that the Pmsdenfauna more closely resembles the
Chester fauna of the Heath thanany Pennsylvanian fauna, the
msden was designatedas late Chester (Scott, 1935>.
Following establishment of thetripartite Big Snowy Group, the main arguments involving BigSnowy nomenclature have focused on: (1) attempts to expand thegroup to include additional units,
(2) correlation of the BigSnowy Group with time and strati- graphically equivalent units tothe west,(3) the recognition of disconformities and erosionalunconformities within and between the
Mississippian and Pennsylvanianage strata, and (4) revisions of the stratigraphic position of theMississippian-Pennsylvanian boundary which involve the top of theBig Snowy Group. 30
The Charles Formation conflict
In a well drilled in 1941 on the Cedar Creek anticline in southeastern Montana, a series of interbedded limestones, dolomites, anhydrites, and subordinate shales were encountered between the
Madison Group and Kibbey Formation. This unit was subsequently called the Charles Formation and added to the base of the Big
Snowy Formation, immediately below the Kibbey Formation (Seager,
1942). The Charles was offered as a possible depositional bridge, spanning the time between deposition of the upper part of the
Madison and the lowermost Kibbey. The widespread development of porosity in the upper part of the Madison was considered indicative of a time break and resulted in inclusion of the Charles in the Big
Snowy Group (Seager, 1942).
As the areal extent and lithological character of the Charles became more clearly understood, several workers countered the previously held notion that it represented initial Big Snowy deposition. Perry (fide Hadley, 19ø), for instance, considered the
Charles as a drying up phase at the end of Madison deposition.
Brecciated fragmental limestones at the top of the Madison Group, and surface exposures of dense to saccharoidal dolomites (often colored pink to red),containing brecciated zones were subsequently correlated with the subsurface evaporitic Charles (Hadley, 1950;
Sloss, 1952).
Analysis of the Madison Group and the Brazer Limestone to the west resulted in the recognition of the depositional contemporaneity of the upper parts of these units with the Charles of central and eastern Montana (Hadley,1'350; Sloss and Moritz, 31
1950), meriting inclusion of the Charles as the uppermost formation
in the Madison Group. additionally, the Kibbey rests with marked
unconformity on the eroded and channelled surface of the Charles
or the Mission Canyon near the margins of the Williston basin,
establishing that a brief period of uplift and/or hiatus preceded
deposition of the Kibbey Formation (Sloss, 1952).
The Mississippian-Pennsylvanian boundary problem
Pccurate positioning of the Mississippian-Pennsylvanian boundary on paleontological grounds has been a problem ever since
Weed (1900) first assigned a Lower Carboniferous age to the
Quadrant Formation on uncertain fossil age determinations.
Subsequent to the establishment of the Big Snowy Group and
Amsden Formation as Mississippian, Scott (1945a, b) presented the first concrete evidence of a Pennsylvanian age for the upper part of themsden Formation, following discovery of a primitive fusilinid, the genus Millerella (this genus is now known to span latest Mississippian through Pennsylvanian time). Willis (1959) then lowered the boundary to a stratigraphic position coincident with the Heath-Tyler contact (the name Tyler was used earlier by Mundt
(1956) to supplant the Lowermsden Formation). Lowering the boundary to the top of the Heath was justified by the reported presence of an unconformity or scour zone at the base of the
Tyler, and by the identification of a fauna in the Tyler of known
Pennsylvanian affinity elsewhere (Willis, 1959).
In the same year, Gardner (1959) refuted the regional unconformity at the top of the Heath Formation, and expanded the 32
Big Snowy Group to include the overlying Cameron Creek, laska
Bench, and Devils Pocket Formations, the
first and last of these replacing the Tyler and tmsden/Tensleep of
Mundt (1959), respectively. Gardner (1959) concluded that Mundt's
(1959) erosional unconformity is actually a conformable
Heath-Cameron Creek transition containing isolated channel
deposits, and that the revised Big Snowy Group represents one
essentially uninterrupted cycle of deposition.
Easton (1962) subsequently maintained the Big Snowy
terminology of Gardner (1959), but noted a transitional
Mississippian-Pennsylvanian character in the faunas of the Tyler
Formation and laska Bench Member of the Amsden Formation. He
also reestablished the regional unconformity on top of the Heath.
in a later report, Maughan and Roberts (1967) advocated an
exclusively Mississippian age for the Big Snowy Group of Scott
(1935), and a Pennsylvanian age for the overlying Ameden Group, as
Willis (1959) had proposed earlier. Unlike Gardner (1959), Maughan
and Roberts (1967) favored two cycles of deposition interrupted by
a widespread erosional unconformity to explain the
lithostratigraphic relationships of the Big Snowy andmsden Group
rocks. The Heath-Tyler unconformity is not well exposed in most
areas, although substantial evidence is afforded in exposures in the
Little Belt and Little Snowy Mountains in central Montana arid in
the subsurface of eastern Montana (Maughan and Roberts, 1967).
Maughan and Roberts (1967) established the time equivalence
of the Big Snowy-msden Group lithostratigraphic boundary and the
Mississippian-Pennsylvanian system boundary on two points of 33
evidence. First, they commented,
"It is believed that this unconformity was formed nearly contemporaneously with that unconformity which, by definition..., separates these two systems in the Mississippi Valley. The paleontologic evidence in Montana seems to confirm this accepted position."
Second, re-evaluation of Easton's (1962) fossil collection in
consideration of this hypothesis indicated a Pennsylvanian age for
those rocks which Easton had determined to be transitional, either
Mississippian or Pennsylvanian in age, or both. To the
time-equivalent rocks in southwestern Montana they assigned the
name Big Snowy Formation, as differentiation of the Kibbey, Otter,
and Heath Formations is not possible there.
The work of Maughan and Roberts (1967) has formed the basis
of nomenclature for all subsequent work in Montana. Differences
of opinion have recently arisen again, however, regarding the
placement of the system boundary. Maughan and Roberts (1967)
acknowledged that fossil evidence for a Pennsylvanian age in the
Tyler was limited, but nonetheless contended that the unconformity
at the base of the Tyler represented the best horizon in the field
for locating the boundary. Brachiopod, conodont, and foraminifera
biostratigraphy has recently indicated, however, that the system
boundary in central Montana is located within the Alaska Bench
Limestone of the Amsden Group, well above the horizon advocated
by Maughan and Roberts (1967; Davis, 1983; Dutro et al., 1984;
Wardlaw arid Pecora, 1985).
Relationship of the Big Snowy Formation to the underlying Mission Canyon Limestone
The Mission Canyon Limestone is a prominent cliff- and 34
ridge-forming limestone of middle Osage to middle Meramec age
(Sando, 1975). This unit is present in much of Montana, but is
thin or absent locally and north of 47°N latitude, where it has
been removed by pre-Jurassic and/or Tertiary uplift and erosion.
In southwestern, central, and eastern Montana the formation is
overlain by the Big Snowy Group or Formation, while farther south
the msden Formation rests with marked disconformity on the
Mission Canyon.
Mission Canyon time was characterized by several fluctuations
of sea level, resulting in the deposition of cyclically interbedded
dolomite and limestone, with local anhydrite intervals in the upper
half of the formation (Roberts, 1966). Thickness trends in the
Mission Canyon correspond to those of the Big Snowy, being
thickest in the Snoworest and Big Snowy troughs, and thinning to
the north and south (Craig, 1972).
Solution breccia zones are conspicuous features in the upper
Mission Canyon and can be traced throughout most of the mountain
ranges in southwestern Montana, as well as in the subsurface of the Big Snowy-Williston basin area. In the latter region the upper
part of the Mission Canyon is replaced by the Charles Formation
(Sloss, 1952). Several brecciated zones in nearby surface exposures of the upper Madison Limestone correlate with unaltered anyhydrite zones in the subsurface, indicating a direct relationship between
Late Cretaceous and early Tertiary uplifts and the areal extent of the solution breccia zones (Severson, 1952; Nordquist, 1953; Roberts,
1966).
Karst features, such as sinkholes and enlarged joints, 35
perpendicular and parallel to bedding, are the two most commonly observed features at or near the Mission Canyon-Big Snowy contact
in southern and southwestern Montana; caves occur less frequently
(Sando, 1974). Features observed along the Mission Canyon-Big
Snowy contact generally substantiate an erosional unconformity in southwestern Montana. Irregular contacts, erosional thinning, and silicified limestones in the uppermost Mission Canyon, and limestone pebble conglomerates in the lowermost Kibbey are reported at various localities within the Snowcrest trough area (Scholten et al.,
195; Blake, 19Z9; Pecora, 1981; Guthrie, 1984). Workers in the
Snowcrest Range area usually have argued against the presence of an unconformable relationship here; however exposures of this relationship are very poor.
Big Snowy trough
Kibbey Formation
The Kibbey Formation, the oldest and most widespread of the three formations in the Big Snowy Group in Montana, represents nearshore deposition at the leading edge of the transgressing Big
Snowy sea. In the Big Snowy trough and Williston basin areas the
Kibbey is divided into three informal members (Harris, 1972).
The lower member consists predominantly of red arid green shales, with thin to thick sandstone and gypsum lenses. Sand, derived from the craton, accumulated in high energy shoreline deposits, while deposition of finer grained detritus was occurring in intertidal and very shallow subtidal environments. Periodic restrictions of marine circulation in the trough, related to tectonic 36
instabilities and/or fine-scale eustatic sea level fluctuations, resulted in gypsum deposition locally (Ballard, 1964, Sando, 1976).
The subsequent diminution of the supply of coarse clastic material from the cratonic interior promoted deposition of the succeeding dolomites, evaporites, and bioclastic limestones which characterize the middle member (Smith and Gilmour, 1979). Q thick sequence of sandstones, interbedded red and gray shales, and subordinate lenses of dolomite make up the upper member, completing the threemember series. The sandstones of this upper member were deposited in a high energy shoreline environment concurrent with deposition of shales in the deeper, quieter waters in the central part of the trough (Ballard, 1964; Smith and Gilmour,
1979).
The exact age of the I Sando et al., 1975). Otter Formation The Kibbey Formation is conformably overlain by the Otter Formation. The gradational transition is best exposed at Durfee Creek dome, in the Big Snowy Mountains, where red sandstones of the upper Kibbey member intertongue with gray shales of the basal Otter over a 10 to 20 foot interval (Harris, 1972). The Otter, assigned a Chester age,is characterized by a lower shale and limestone sequence, a middle limestone and evaporite sequence, and an upper black to green shale succession. deeper water, normal 37 marine deposit ional environment, punctuated by a brief period of very minor clastic input, is envisioned during Otter deposition (Harris, 1972). Heath Formation The contact with the overlying Heath Formation is set at an abrupt color change in the shales from bright coppery green to black, which is generally coincident with the occurrence of a limestone bed rich in productid brachiopods (Easton, 1962). In some areas the color change is less abrupt, occurring over a 33 to 100 foot interval, and the top of the Otter is placed at the horizon above which the shale and limestone litholgy typical of the Otter is replaced by a predominance of black shales common to the Heath (Smith and Gilmour, 1979). The Heath Formation records the climax of marine transgression in the Big Snowy trough in late Chester time, and the rapid withdrawl of the the sea which followed (Fig. 9). The Heath consists chiefly of dark gray to black carbonaceous claystones and niudstones, which commonly are fissile on outcrop, and interbedded thin to massive beds of dark gray, argillaceous limestones and dolornites (Maughan, 1984); both the shales and limestanes tend to be petroliferous. Coarse, terrigenous material, common to the Heath Formation, distinguishes it from the less clastic-enriched Otter Formation below. The lower part of the Heath was deposited in calm, relatively deep water, while the erosionally thinned uppermost part of the formation, distinguished by isolated gypsum beds, reflects the shallow and partially restricted conditions prevalent during rapid withdrawl of the sea in latest Chester time (Maughan, 1984; Sando, 1976). The top of the Heath Formation is placed at a regional unconformity on which rest uppermost Mississippian Tyler Channel sandstones, or sandstones, limestones, and silty shales of the Cameron Creek Formation (Fanshawe, 1978). The Big Snowy Group is generally considered to be representative of a deepening upward sequence coincident with eastward transgression of the Big Snowy sea. This vertical change is also observed laterally in both the Big Snowy and Snowcrest troughs, suggesting that the Big Snowy units represent a classic d iachronic sequence. Several points of evidence suggest that the Kibbey, Otter, and Heath Formations are, at least in part, facies equivalents of one another (Fig.11). First, the contacts between the three formations are gradational over several tens of feet, and commonly intertongue throughout the deposit ional basin (Maughan and Roberts, 1967). Exceptions to this are noted at the basin margins, where fluctuations in the transgression resulted in the development of local disconformities. Second, biostratigraphic data and stratigraphic relationships indicate that the Kibbey is oldest near the Idaho-Montana border, and youngest in the eastern end of the Big Snowy trough (Fig. 9; Sando, 1976). This age variation helps to explain the areal extent and thickness patterns of each of the formations in the Big Snowy Group. The Kibbey is the most widespread of the three units and NORTH 80 U T H TIM Fm. MacgIao Limestone Lln. Of time $Yfl0hroou8 Figure ii. Schematic cross section acros5 the Big Soy trough, showing gross facies re1atioflahA5 and diachror,ic nature of the Big Snowy Group formatjon Littiologies are generalized (from Harrj5, 197a). (A) 40 is thickest along the basin margins, whereas the Heath is the most restricted areally, but is thickest in the center of the basin (Harris, 1972). The Heath and Otter are both observed to thin laterally in almost direct proportion to thickening of the Kibbey toward the paleoshore (Maughan, 1984). Snowcrest trough The Snowcrest trough is recognized as a unique entity, intimately related structurally and temporally to the Big Snowy trough, and, yet, bearing a relatively unique Upper Mississippian rock sequence. Several workers mapped the Carboniferous age rocks in southwestern Montana in the early fifties (Honkala, 1949; Keenmon, 1950; Kupsch, 1950; Mann, 1950, Gealy, 1953), but only recently have geologists again directed their attention to this area. Oil exploration in this region has been minimal, probably because of the poor data base, complex structural fabric, and discouraging results of early wildcat wells. Recent work has resulted in the development of new stratigraphic nomenclature for the Upper Mississippian and Lower Pennsylvanian rocks in southwest Montana, and is providing insight into the relationship of the Big Snowy Formation in the Snowcrest trough and the Big Snowy Group in the Big Snowy trough. Southwest of the Lombard arch region (Fig. 7) the unique stratigraphic identity of the Kibbey, Otter, and Heath Formations of central Montana becomes obscured. The lower and upper members of the Kibbey Formation thin over the Lombard arch and 41 continue essentially unchanged to the southwest, whereas the middle member thins to a feather edge on the eastern side of the arch (Harris, 1972). The overlying Otter and Heath Formations also thin over the arch, but the individuality of each is lost as they pass laterally into a single unit dominated by dark gray limestone (Fig. 9). Blake (1959) tentatively named this unit the Lombard facies of the upper Big Snowy Group because of its accessibility and well developed exposure near the abandoned Lombard railroad station, located approximately 1! miles south-southeast of Townsend, Montana, along the Missouri River. At this location the rocks are chiefly gray to black silty limestones with thinly laminated silty partings, and silty claystones. McMannis (1955) first recognized this unit in the Bridger Range, where he correlated it to both the Lombard section, to the northwest, and the type Big Snowy rocks in the Big Snowy trough. Subsequent workers have reduced the Big Snowy Group in the Snowcrest trough to format ional status, because the individual formations of the group cannot be mapped separately (Maughan and Roberts, 1967). Locally, the Otter Formation has been traced as far west as Three Forks (Terry, 1953), although west and southwest of the Castle Mountains area the percentage of silty limestone increases markedly at the expense of shale, making recognition of the type Otter and/or Heath Formations extremely tentative (Blake, 1959). 42 New Terminology Most recent workers in this region have attempted to apply the type Big Snowy terminology to the Upper Mississippian rocks in their respective field areas, but the need for revision in the terminology for rocks at this stratigraphic level is mentioned by all. New stratigraphic nomenclature has been adopted by the U. S. Geological Survey for Upper Mississippian and Lower Pensylvanian strata in southwestern Montana and east-central Idaho to supplant the Big Snowyand Amsden Formations (Fig. 9; Wardlaw and Pecora, 1985). The new group is be called the Snowcrest Range Group, although, unfortunately, none of the type section localities are actually in this range. Sawtooth Mountain, in the southwestern part of the Snowcrest Range, is an ideal location to measure and describe rocks correlative to the Lombard Limestone facies of the Big Snowy Group, described by Blake (1959). The Lombard Limestone, the middle unit of the proposed Snowcrest Range Group could possibly be supplanted by the "Sawtooth Mountain Formation" or "Snowerest Formation" to maintain integrity with the code of stratigraphic nomenclature. Kibbey Formation (revised) and Lombard Limestone. The Kibbey Formation, assigned a middle Meramec age,is retained as the basal formation in the new group (Sando et al., 1985). This is conformably overlain by theLombard Limestone (new), which is correlative to the Otter and Heath Formations, and part of the Tyler Formation of central Montana. The Lombard consists of a series of thin- to thick-bedded lime mudstones, wackestones, and 43 packstones with silty to limy shale interbeds and partings (Wardlaw and Pecora, 1985). A late Meramec to Chester age is assigned to this unit. At some localities a lower and upper member can be recognized, but this differentiation is lost to the west. Canover Ranch. The uppermost unit is the Conover Ranch Formation, correlative to the upper part of the Tyler Formation and the Alaska Bench Limestone in central Montana (Fig. 9). Within the Snowcrest trough, it is, in part, temporally equivalent to the lowermost part of the Pennsylvanian Quadrant Formation. This unit displays a more variable lithology, consisting of pale reddish mudstones, and subordinate marine limestone and sandstone beds which crop out discontinuously. Faunal evidence suggests a late Chester age for these rocks, although the unit becomes progressively younger to the north and northeast, ultimately acquiring an early Morrow age (Wardlaw and Pecora, 1985).It is, therefore, apparent that the Mississippian-Pennsylvanian boundary lies within the upper part of the Conover Ranch, because this unit is time equivalent with the Alaska Bench which is known to contain the system boundary in central Montana (Davis, 1983). Railroad Canyon Formation. The Railroad Canyon is the new name proposed by the U. S. Geological Survey to supplant the Big Snowy Formation in easternmost Idaho (Wardlaw and Pecora, 1985). This formation, found only in the Beaverhead Range, consists of dark shales, limy mudstones, fossiliferous silty limestones, and clayey calcareous siltstones, with subordinate sandstones and conglomeratic 44 limestones. It is laterally equivalent to the upper half of the Snowerest Range Group in southwestern Montana (Wardlaw and Pecora, 1985). This report uses the terminology of Wardlaw and Pecora (1985) inasmuch as this nomenclature best conforms to the rock units described in this report. Relationship of the Big Snowy Formation to the overlying Amsden Format ion The Big Snowy Group is overlain by the late Chester to Morrow Conover Ranch Formation and Pmsden Group in the Snowcrest and Big Snowy troughs, respectively. The contact between these two groups varies, however, from conformable at the southwesternmost end of the Snowerest trough to unconformable in the Big Snowy trough and northeastern end of the Snowcrest trough. The unconformity is attributed to withdrawl of the Big Snowy sea to a position in southwestern Montana in late Chester time. This relatively short-lived marine regression was associated with sporadic, differential uplift in the Big Snowy trough (Sando, 1976). Pt sornà places in the Big Snowy trough depositionacross the Big Snowy-Amsden boundary appears to have been continuous (Jensen and Carison, 1972). The Tyler Formation, distinguished in part bygray and red siltstones and sandstones, unconformably overlies the Big Snowy Group in central Montana (Flaughan and Roberts, 1967). tipper Big Snowy rocks in the southern and central parts of the Snowcrest trough are overlain by the predominantly red sandstones,siltstones, 45 and mudstones of the Conover Ranch Formation, the correlative of the Tyler Formation (fig. 9; Wardlaw and Pecora, 1985). The generally poor exposures in southwestern Montana have prevented agreement among investigators regarding the characteristics of this contact in the Snowcrest trough area southwest of the Bridger Range. Recent work in the Blacktail Mountains has suggested that the Conover Ranch conformably rests upon the Lombard Limestone at the southwestern end of the Snowcrest trough (fig. 9; Pecora, 1981). In the Beaverhead Mountains, the Railroad Canyon Formation, correlative to the upper half of the Lombard Liraestone, is conformably overlain by the Bluebird Mountain Formation. The lower part of the Bluebird Mountain is correlative to the Conover Ranch, and like the Conover Ranch, represents a flood of inner craton-derived sand during latest Chester time (Skipp et al., 1979; Wardlaw and Pecora, 1985). The conformity-unconformity transition must, therefore, occur somewhere within the central or south- western parts of the Snowcrest trough. 46 RELATIONSHIP OF THE KIBBEY FORMATION TO THE UNDERLYING MISSION CANYON LIMESTONE Description The Mission Canyon Limestone crops out throughout most of the thesis area, although southeastward thrusting and associated folding has locally removed and/or added section. Rocks of the Mission Canyon Limestone and Snowcrest Range Group make up most of the western flank of the Snowcrest Range. The most complete Mission Canyon section crops out at the southwestern end of the range, near Red Rock River (NW 1/4, section 21, 7.13 S., R. 7 W.), approximately 6.4 miles due east-northeast of Lirna, Montana. At this location, 1,327 feet of Mission Canyon are exposed in a S. 27 E.-striking ant icline. The limestones and dolomites in the lower half of the formation crop out discontinuously and vary from massive to crudely medium- to thick-bedded. The exposed upper half, 448 feet thick, is characterized by well developed, thin to very thick beds which display more lateral continuity than those below. A poorly exposed solution collapse breccia, which can be traced laterally for almost one half mile, occurs midway up the section. In addition to a sharp increase in slope, the bedding character of the carbonates changes dramatically across this breccia zone; thus the breccia acts as a dividing line between the lower and upper sections. The lower section, approximately 54 feet thick, is composed of biopelniicrites, sparse biomicrites, echinoid biosparites, and micrites. This diversity of lithologies (determined by petrographic 47 analysis) is commonly difficult to recognize in the field, as many of the rocks are partly to completely recrystallized and most are extensively fractured. As a result, these rocks are classified in the field as sparsely fossiliferous wackestones, mudstones, and recrystallized carbonates (Dunham, 1962). Fresh surface colors vary from grayish brown (5 YR 4/2), to light brownish gray (5 YR 6/1), to pale brown (5 YR 5/2), but the majority of the rocks weather to either light gray (N7) or medium light gray (N6). The uppermost Mission Canyon is covered and estimated to be 264 feet thick. The upper section is less diverse lithologically, consisting of a thickening upward sequence of washed biomicrites and sparse biomicrites, with thin, subordinate dolomite and/or dolamitic limestone interbeds. This sequence crops out as pronounced, laterally continuous to discontinuous, planar to slightly undulatory ledges. Cliffs occur locally because of the steep, southeastward dip of the beds on the east-facing hillside. The top of this exposed sequence ends abruptly at the base of the hillside, passing into a wide, covered saddle underlain by Kibbey, Lombard, and Amsden lithologies (fig. 4). This covered, saddle-forming interval is ubiquitous throughout the soutwestern end of the Snowerest Range. Approximately 543 stratigraphic feet of cover separate the highest Mission Canyon exposure from the lowest Lombard exposure. Most of the gray to dark gray soil and float across this interval is of Mission Canyon and Lombard affinity; however, a narrow, diffuse zone of admixed buff to grayish orange soil occurs midway between the two exposures in thesaddle area (NE 1/4, section 21, T. 13 9.,R. 7 U.). This narrow zone probably represents the non-resistant Kibbey Sandstone. Because the top of the Mission Canyon here is obscured by float and/or soil development, analysis of the contact with the Kibbey is not possible. The solution breccia zone is significant, however, as stratigraphically restricted carbonate breccia zones are common in the upper two-thirds of the Mission Canyon in the western Rocky Mountains region, and can often be utilized as regional stratigraphic markers (Sando, 1968, 1974; Roberts, 1979). Solution breccias have been reported as low as 600 feet below the top of the Mission Canyon in the Bridger Range (Guthrie, 1984), and from 80 to 360 feet below the top in northern Wyoming mountain ranges (Sando, 1974). Pecora (1981) reported the occurrence of a 70-foot-thick breccia zone approximately 250 feet below the Mission Canyon-Kibbey contact in the Blacktail Mountains, northwest of the thesis area. The solution breccia zone at the Red Rock River section occurs 448 feet below the uppermost exposed Mission Canyon ledge (712 feet below the inferred Mission Canyon-Kibbey contact). The thickness of the solution breccia varies laterally, primarily involving assignment of the upper contact, but averages 33 feet. The base is sharp and planar, as the underlying limestone lithology terminates abruptly against the poorly exposed solution breccia interval, coincident with a moderately sharp change in slope and soil color. Most of the unit is covered, but trenching and exploration in and adjacent to gopher holes reveals the underlying brecciated lithology. The pale yellowish orange (10 YR 8/6) to moderate yellowish brown (10 YR 5/4) soil is typically thin. The underlying 49 lithology is dominated by limonite- and/or goethite-stained limestone solution breccia. Vuggy porosity is ubiquitous, although the amount of porosity varies dramatically, from 8 to 40 percent, over a very short distance, both laterally and vertically. Many of the irregular vugs exceed 1/2 inch in diameter and are filled with botryoidal calcite masses. Variably sized, subangular to angular limestone and dolostone fragments are common, although many have been leached, creating a honeycomb-like texture composed of the surviving coarse interciast spar cement. Petrographic analysis reveals that the limestone clasts are all recrystallized, unfossiliferous(?) limestone (some dolomitic), containing six percent medium to coarse quartz silt. All of the breccia clasts are characterized by a light yellow to light orangish red iron stain which intensifies toward the outer edge of the clasts. Analysis with reflected light indicates that the stain is goethite and/or hematite, the latter occurring chiefly along the clast margins. Additionally, the edges of many of the coarse calcite cement crystals between the angular clasts are iron stained. The vuggy porosity is restricted to the clasts. The cement is predominantly coarse, mosaic, limpid sparry calcite which, upon preferential solution of the breccia clasts, creates the polygonal, honeycomb-like texture seen in hand sample. Clear sparry calcite cement does not occupy the entire interciast area. Fine, angular limestone fragments commonly surround the larger limestone cl.asts. Locally, pockets of subrounded, rnonocrystalline quartz silt and very fine sand (total 48 percent) and iron-stained microspar and pseudospar (total 42 50 percent) are present. Intergranular and vuggy porosity make up 15 percent of this matrix. Detrital zircon and chart occur rarely. Near the top of the solution zone the breccias grade upward into thin, fractured limestone beds with thin, pale red (10 R 6/2) to pale reddish brown (10 R 5/4) dolomitic siltstone iriterbeds. Monocrystalline quartz and dolomite make up 63 and 30 percent of the total constituents, respectively, followed by six percent chert and one percent polycrystalline quartz. In contrast to the absence of heavy minerals in the lower part of the breccia zone, a diverse assemblage occurs in the red siltetones. Magnetite, tourmaline, zircon, green hornblende, leucoxene (after ilmenite), and augite(?} all occur as scattered grains in the predominantly quart zose framework. The diameters of the quartz grains range from 0.02 mm (medium silt) to 0.28 mm (fine sand), most occurring in the very fine sand size fraction (averaging 0.10 mm diameter). P similar range of values characterizes the chart fraction, but the chart grains display a subrounded to rounded habit and have high sphericity values (0.8-0.9), in contrast to the quartz grains which are typically subangular to subrounded and more tabular/elongate (sphericity = 0.5-0.7). Dolomite is present as a dirty, coarse, mosaic matrix and cement. Poorly developed, limpid to dusty dolomite rhombs occur locally. In addition to the cementing dolomite, numerous syntaxial quartz overgrowths cement many of the framework constituents. Hematite staining is ubiquitous, but usually incomplete, on the edges of the framework elements; the iron stain never occurs 51 within the quartz or chert grains. very complete and intense peripheral iron stain locally colors both the framework constituents and the dolomitic matrix. Laminations are very rare and usually irregular. Most of these thin siltstones are massive, but display irregular banding patterns because of local variations in hematite concentration. Upsection the highest thin siltstone bed is overlain by limestones which become progressively less fractured, ultimately passing into the thin to medium beds which characterize the lower part of the upper half of of the Mission Canyon sequence. approximately 12.7 miles to the northeast, at Clover Divide, the uppermost Mission Canyon is exposed on the southeast flank of a large, northeast-trending anticline (NW 1/4, section 23, T.12 S., R. 6 W.). The Mission Canyon here is exposed as a series of ledges and cliffs exposed by antecedent stream erosion and road construction normal to the strike of the anticlinal structure. Elsewhere this section is predominantly covered and vegetated. Late Cretaceous to early Tertiary uplift and associated subaerial exposure has resulted in the development of a modern karst topography, including limestone spires or hoodoos, solution pits, small caves, and extensive vuggy porosity, which overprint the paleokarst deposits here. The absence of any beds or soil indicative of the Kibbey Formation at this locale, and the presence of a stream valley which contours the inferred Mission Canyon-Lombard contact, suggests that the Kibbey has been faulted out in this area. The lower 1,032 feet of the 2,023 foot thick Lombard section here, superposed on 52 the Mission Canyon, is believed to be fault thickened (Zieglar, 1954; Perry, 1983; this report, appendix P). Paleokarst features arid diagnostic corals in the uppermost limestone beds of the Mission Canyon suggest that very little Mission Canyon Limestone is missing beyond that originally lost to subaerial exposure and erosion in Meramecian time. The upper formal member of the Mission Canyon Limestone in southern Montana and northern Wyoming is the Bull Ridge Member. This member is characterized by a basal, silty to dolomitic, limestone solution breccia. This grades upward into a sequence of fossiliferous limestones and dolomites, commonly containing many karst elements, including enlarged joints, caves, sinkholes, and solution breccias (Sando, 1968, 1972, 1974a,b). The partial Mission Canyon exposure at Clover Divide similarly consists. of a thick sequence of poorly to well exposed, sorted biosparites, and sparse and packed biomicrites, with subordinate silty dolostone and calcareous siltstone interbeds. Biotic constituents include echinoid ossicles and plate fr'agments, brachiopods, pelecypods, foraminifera, ostracodes, trilobites, corals, and bryozoan debris. Pellets and intraclasts occur locally. Within this limestone sequence, solution breccias, pisolitic limestones, collapse structures, and large, discontinuous solution cavities filled with massive, pale yellowish orange to moderate red, argillaceous and dolomitic siltstones and silty carbonate breccias are all common. The uppermost fossiliferous limestone beds contain two significant corals, Diphyphyllum sp. and Vesiculophyllum sp. (W.3. Sando, personal communication, 1985) of Osagean to 53 Meramecian age.. The uppermost fossiliferous limestone beds in the Bull Ridge Member type section also contain, and are characterized by Dihyphy1lum sp. which is diagnostic of Coral Zone III (early Meramecian; Sando, 1968, 1980a, 1982). The solution breccias display a complex genesis, involving several periods of brecciation, neomorphism, and recrystallization in both the limestone clasts and surrounding calcareous matrix. Dolomite content in the matrix varies, but is characteristically very low (<10 percent). Likewise, the quartz fraction is generally subordinate to the mosaic pseudospar and sparry calcite. Most of the quartz present is coarse silt (average diameter = 0.03 mm), although coarse sand quartz grains (up to 0.8 mm) occur rarely. X-ray diffraction analysis of the matrix indicates the additional presence of kaolinite. While the quartz fraction is subordinate in the matrix, many of the large, sparry calcite-filled fractures contain a significant amount of raonocrystalline, angular to subrounded, quartzose silt. In outcrop, the small, randomly oriented limestone blocks and variably rounded clasts show little ordered vertical variation in size within the breccias. Many of the clasts have altered to a soft, grayish orange (10 YR 7/4) clay material which locally is weathered out, creating irregular vugs. In several places the honeycomb-like vuggy habit, similar to that described in the solution breccia at the Red Rock River section, is very pronounced. In contrast, however, the vugs here tend to be lined with clays rather than botryoidal calcite. t a few exposures the clasts display a crude reverse grading, passing upward into unfractured limestone beds. 54 These solution breccias are seldom stratigraphically bound and rarely display moderately disturbed, but intact, limestone interbeds of variable thickness. Unlike the solitary solution breccia zone found at Red Rock River, the myriad of solution breccias and other karst features have disrupted much of the bedding at Clover Divide. Discontinuous solution cavities are especially common. Massive, silty dolostones and lirnestones, and brecciated calcarec'us siltstones and subordinate sandstones typically fill these cavities. Many of these karst fills are very deeply weathered and exhibit a pale yellowish orange (10 YR 8/6) to moderate red (S R 4/6) color. Calcite is more common than dolomite, and quartz typically is slightly subordinate to the microspar and pseudospar, although quartz locally makes up a more significant part of the rock. Chert is always rare. As in the matrix of the solution breccias, kaolinite is present in these rocks. Muscovite, is a common accessory mineral, succeeded by rare zircon and epidote grains. Small, irregular patches of coarse sparry calcite occur locally, and may represent recrystallized mollusks or some other indeterminate bioclast. Collapse structures are ubiquitous and several excellent examples can be found within the uppermost Mission Canyon outcrops. Bedding is commonly fractured, distorted, faulted, and/or missing from solution of underlying and overlying units and subsequent collapse and flowage. The range in size of the brecciated limestone fragments is wide, and sorting is very poor. At several exposures columns of large, angular limestone blocks surrounded by contorted, finely brecciated silty limestone, dissect 55 or disrupt the otherwise intact, well bedded limestories below (fig.12). Sinkholes, characterized by steep-walled, widening-upward shapes and predominate red sandstone, siltstone, and/or shale inf ill, are commonly found throughout south-central Montana and northern Wyoming (Sando, 1974). These paleokarst features, however, were not recognized at Clover Divide, or elsewhere in the range. The actual contact between the Mission Canyon Limestone and the Kibbey Formation cannot be observed anywhere in the Snowcrest Range because of faulting and the non-resistant character of the Kibbey. The presence of solution breccia zones, collapse structures, and solution cavities along discrete stratigraphic horizons within Meramecian limestones and subordinate dolomites (uppermost Mission Canyon) suggest that a period of subaerial exposure and solution by meteoric waters percolating through the carbonates occurred subsequent to Mission Canyon deposition, but before Kibbey or Lombard deposition. Exposure of this contact is also poor at Sheep Creek Canyon, in the Blacktail Mountains, but an abrupt transition from ledge-forming, fossiliferous limestone to non-resistant, siltstone and silty dolostone does occur. Because of the predominantly covered habit of the Kibbey, specific relationships between the two units along the contact cannot be determined. The uppermost Mission Canyon bed displays a discontinuous outcrop habit along strike, however, and locally the grayish orange (10 YR 7/4) to moderate yellowish brown (10 YR 5/4) soil cover, overlying the vertical limestone bed, appears to fill the gap between ledges. The gentle 1! '.4' Figure 12. Solution collapse breccia at Clover Divide. Note large coherent limestone blocks "floating" in sandy limestone to dolostorie rnatri. Silty limestone bed is locally truncated ard folded by collapse structure. Hammer at left edge of breccia for scale. 57 profile of the hillside does not exclude the possibility that the grayish orange cover is not in situ, and occurs in these gaps because of normal surface erosion, weathering, and transport processes. In addition to the sharp contact, Pecora C1981) has located one exposure in this area characterized by a dusky to moderate red quartz conglomerate with a silty matrix which overlies Mission Canyon limestones. Interpretation The poor to non-existent exposure of the Mission Canyon-Kibbey contact in the Snowerest Range precludes precise description of the depositional relationship between these two units in the thesis area. Exposure in the Blacktail Mountains, and the presence of paleokarst elements in the uppermost part of the Mission Canyon exposed in the southern part of the Snowcrest Range, however, suggest complete withdrawl of the Madison sea from the thesis area in late early Meramecian to early middle Meramecian time. The Mission Canyon Limestone in southern Montana and northern Wyoming is divided into three members. These members, in ascending order, are the lower limestone member, the middle cliffy member, and the Bull Ridge Member (Sando, 1972). The middle cliffy member is characterized by a ubiquitous, 25 to 50-foot-thick, basal solution breccia ("lower solution zone" of Sando, 1967), overlain by a variable sequence of cliff-forming limestones. The lower limestone member lacks solution breccia zones, is commonly thick-bedded, and contains a sparse fossil assemblage. The uppermost member, the Bull Ridge Member, also contains a basal solution breccia ("upper solution zone"), 10 to 25 feet thick, but is overlain by a sequence of brecciated fossiliferous limestones containing a diverse assemblage of early Meramecian fossils (Diphyphyllum Zone or Coral Zone III); several thin terrigenous intervals commonly occur within the limestone sequence, as well (Sando, 1974). The Mission Canyon Limestone in the northern and central parts of the Snowcrest Range is structurally complicated by one or more thrust faults which variably superpose slivers of Mission Canyon against Lombard Limestone, eliminating the uppermost Mission Canyon, and/or Kibbey, and/or lowermost Lombard from the exposed upper Paleozoic sequence. The two partial Mission Canyon exposures in the southern part of the range, howver, can be schematically combined to create a nearly complete section, which can be subdivided into three sequences correlative with the Mission Canyon type members. The lithology and bedding habit of the lower and upper exposed parts, respectively, of the Mission Canyon sequence at Red Rock River, separated by a medial solution breccia, can be informally correlated to the lower limestone and middle cliffy members of the type Mission Canyon. The sequence exposed at Clover Divide can,in turn, be correlated with the Bull Ridge Member, based on the fossiliferous limestone and subordinate dolomite sequence containing DiphyDhyllum sp. and Vesiculophyllurn sp., with local siltstone and silty limestone interbeds. Given it stratigraphic position, apparently unfaulted setting, and overall less 59 resistant character, the thick covered interval between the uppermost and lowermost exposed Mission Canyon and Lombard, respectively, at the Red Rock River section, is also inferred to be correlative with the Bull Ridge Member, although its exact thickness is unknown. The presence of Diphyphyllum sp. and Vesiculophyllum sp. in the uppermost Mission Canyon lirnestones indicates that shallow marine deposition was still occurring in this area during early Meramecian time (Coral Zone lilA) and possibly into early middle to middle Meramecian time (Coral Zones IIIB and C; Sando, 1980; Sando and Bamber, 1979). These ages coincide with those of the upper part of the Bull Ridge Member type section on the northern part of the Paleozoic Wyoming platform. Deposition was ongoing to the west, in the present Tendoy Range area, into middle Meramecian to early late Meramecian time (Gutschick et aL, 1983, p. 714), but had ceased to the east, near Livingston, Montana, much sooner, possibly by early Meramecian time tSandberg et a)., 198). Interpolation between these two west-east data points, and a minimum date (late early Meramecian) of complete withdraw) of the sea in the southwestern end of the Snowcrest trough, in the present Snowcrest Range area, suggest that a minimum amount of Mission Canyon has been faulted out at Clover Divide. Therefore, the paleokarst features present in the Bull Ridge equivalent here can be directly related to withdrawl of the Madison sea and subsequent transgression of the Big Snowy sea. The timing of the development of the solution features observed in the Snowerest Range is difficult to determine. In his study of the Madison Group in the Livingston, Montana,area, Roberts (1966) noted both laterally continuous solution breccias and discontinuous, strat igraphical ly unrestricted solution features. The former were attributed to solution of evaparite deposits and subsequent collapse of overlying and interbedded limestones, while the latter were classified as karst deposits. Roberts hypothesized that the karst deposits developed during a post-Mission Canyon, pre-msden period of uplift and subaerial erosion, and that the laterally continuous solution breccias formed later, during Late Cretaceous and early Tertiary uplift. Mnalysis of the the clay mineralogies of the matrix of the karst deposits and solution breccias revealed a predominance of kaolinite and illite, respectively. Therefore, the kaolinite suggests extended weathering of ancient soils on the subaerially exposed surface of the Mission Canyon, while i].lite indicates incipient marine deposition without alteration during uplift or brecciation (Roberts, 1966). Subsequent studies elsewhere in the Mission Canyon present different results and, therefore, different conclusions (McCaleb and Wayhan, 1969; Sando, 1974). Clay mineralogy analysis of the aforementioned deposits in a Mission Canyon-Pmsdensequence at the northern end of the Bighorn Basin, in north-central Wyoming, shows that illite is the only clay mineral present in the matrix of both types of deposits (McCaleb and Wayhan, 1969). This points to a common event, which occurred in post-Mission Canyon, pre-Amsden time. X-ray diffraction analysis of the karst deposits in the Bull Ridge equivalent at Clover Divide indicates the exclusivepresence 61 of kaolinite in the matrix. Similar analysis of the solution breccia at Red Rock River, however, is inconclusive. Sando (1974) advocates a common age and origin of the solution breccias and karet features in the Mission Canyon of southern Montan and northern Wyoming. The solution breccia at Red Rock River, however, may have developed during post-Mission Canyon, pre- Tertiary uplift. Given either origin, the terrigenous fraction of the solution breccia must be part of the original depositional sequence, and the brecciation attributed to solution of an evaporite sequence by phreatic freshwater, followed by collapse of the roof rock and thin limestone interbeds. In contrast, karst development and infilling in the uppermost Mission Canyon at Clover Divide probably occurred during post-Mission Canyon, pre-Kibbey time. Discontinuous, and commonly irregular, solution cavities, solution breccias, and collapse breccias, with a hematite-stained matrix of calcite and quartzose silt and sand, suggest a karst origin for these features. The lack of an obvious connection to the surface, and the presence of kaolinite in the yellowish red to red matrix support this hypothesis. The locally abundant quartz silt and sand in the matrix provide evidence that the karst features developed prior to deposition of the Kibbey Formation, as these terrigenous matrix constituents are thought to be derived from the Kibbey. Rapid infi].ling of the open, uncemented or incompletely cemented solution cavities with reworked soil and unconsolidated Kibbey clastics would account for the massive character of the matrix, as well. 62 The brecciated silty limestones and calcareous siltstones were probably part of the original shallow marine deposit ional sequence, as Sando (1974) has noted in north-central Wyoming. Large solution channels, filled with red Kibbey siltstones, sandstones, and subordinate dolostones, occur in the uppermost Mission Canyon northwest of the thesis area, in the Horse Prairie area. These are interpreted as solution and collapse structures which developed along joint systems during post-Mission Canyon, pre-Kibbey uplift and subaerial exposure (W.S. Goodhue, personal communication, 1985). Solution breccias are also reported in this region and just west, in the Prmstead ant icline area. In both areas the Mission Canyon is additionally capped by a silicified solution breccia, up to 70 feet thick (Hildreth, 1981). North and south of the thesis area, on the margins of the upper Paleozoic Snowcrest trough, red sandstones and siltstones of the basal Anisden Formation disconformably overlie the eroded Mission Canyon Limestone (Mann, 1950; Klepper et al., 1957; Sando et al., 1975; Lageson et al., 1979). Pt most of these locations the uppermost Mission Canyon, or Bull Ridge Member, is characterized by solution breccias, karst deposits, and an upper erosional surface with variable relief. Within the Snowcrest Range and Blacktail Mountains, no evidence for intertonguing or a gradational transition between the Mission Canyon and Kibbey is recognized. Rather, a sharp transition with minor relief is found at Sheep Creek Canyon, indicating an abrupt change in deposit ional environmentacross the contact. Solution breccias are also common throughout the upper 63 60 feet of the Mission Canyon in the Blacktail Mountains, and the top of this Bull Ridge equivalent is truncated at a Meramecian erosional surface (Pecora, 1981). Farther east, in the Bridger Range, karst deposits are common, and three to six feet of relief occur along the Mission Canyon-Kibbey contact (Guthrie, 1984). Solution breccias in the Bridger Range also occur as much as 600 feet below the erosion surface. In summary, karst deposits in the Bull Ridge Member equivalent in the Snowcrest Range indicate a period of subaerial exposure, beginning no earlier than late early Meramecian time, prior to onlap of the Kibbey Formation in late middle to late Merameejan time. The contact between these two formations is obscured or faulted out in the thesis area, but adequate exposure of the contact just northwest, in the Blacktail Mountains, supports this hypothesis. Comparison with the Mission Canyon-Kibbey (or -msden) contact and the lithology of the uppermost Mission Canyon (Bull Ridge Member) elsewhere in southwestern Montana also argues for complete withdrawl of the Madison sea from the western end of the Snowcrest trough in Merarnecian time. 64 KIBBEY FORMATION Introduction The Kibbey Formation is covered throughout the Snowcrest Range, with the exception of an isolated outcrop at Sawtooth Mountain.. A poorly exposed Kibbey section crops out along the north side of Sheep Creek Canyon, however, just north of the thesis area in the Blacktail Mountains. Two lithofacies can be recognized at this location, the upper of which can be correlated with the isolated exposure at Sawtooth Mountain. These two lithofacies are a lower, do]ostone unit, and an upper, sandstone unit, deposited in upper intertidal-lower supratidal and lower intertidal to shallow subtidal environments, respectively. The dolostone and sandstone lithofacies can be correlated to similar dolomite-rich and sand- and silt-rich sequences, respectively, throughout southwestern Montana (Plate 2). Description Snowcrest Range Thrusting has largely removed the non-resistant Kibbey Formation from the Paleozoic sequence exposed throughout the Snowcrest Range, although a characteristic grayish orange soil interval occurs locally in the southwestern part of the range. The only Kibbey outcrop recognized in the thesis area occurs at the base of a prominent hill (summit elevation 9,566 feet) underlain by Lombard Limestone, approximately one mile west of Sawtooth Mountain (SW 1/4, NE 1/4, NW 1/4, section 9,T. 12 S.,R. 5 U.). The characteristic covered Kibbey interval here is broken by a 65 twelve foot thick series of discontinuous, medium-bedded, very pale orange (5 YR 8/2) and yellowish gray (5 V 7/2), fine to methum-grained quartz arenite ledges (fig.13). This abbreviated ledge-forming sandstone sequence is laterally restricted, however, and crops out discontinuously for only several tens of yards along strike. This discontinuous habit may be the result of variable cement composition or slight variation in the degree of cementation. Weathering and fracturing of the medium, planar to slightly undulatory beds has created flaggy and slabby rubble, which surrounds the ledges and is scattered for several tens of feet down the hillside. Evidence of cross-bedding, ripples, grading, and bedding plane structures indicative of current/transport direction are absent. Very thin, slightly undulatory. laminations characterize the upper part of this unit, which weathers to grayish orange (10 YR 7/4), in contrast to the lower part which is typically massive to mottled, and weathers to a moderate brown (5 YR 4/4) color. The transitional character between these two units is difficult to discern because of the discontinuous outcrop habit of these sandstones, but appears to be gradational over an approximately two foot thick interval. Both units are well sorted quartz arenites, but variations in grain size and interstitial clay accompany and,in part, account for the textural variations observed in outcrop. Because of the significant textural differences between the lower and upper units, they will be discussed separately. Detrital quartz grains make up both the framework and matrix of the lower unit. The coarser quartz fraction, which accounts for Figure 13. Photograph of isolated Kibbey outcrop (foreground) at Sawtooth Mountain. Note the characteristic grayish orange color of the ledges and float,in contrast to the gray to grayish brown outcrops, float, and soil of the overlying Lombard Limestone (near snowbank). View is the the southwest, on northwest side of hill located just west of Sawtooth Mountain. 67 40 percent of the rock, is subangular to predominantly subrourided, and ranges from coarse silt (0.05 mm diameter) to medium sand (0.50 mm) size (fig. 14). Fine sand size grains, with an average diameter of 0.18 mm, predominate. Most of the coarse quartz grains (35 percent) are rnonocrystalline and unstrained, but undulose, polycrystalline quartz grains (stretched metamorphic quartz of Folk, 1980) make up four percent of the total constituents, succeeded by scarce, well rounded detrital chert grains (one percent. In addition, a few well rounded detrital orthoclase grains are locally present. No imbricat ion or pronounced shape fabric is recognized, as most of the detrital grains are moderately spherical (average * 0.7), although the subordinate elongate fraction (sphericity = 0.3-0.5) does display a crude orientation subparallel to bedding. The matrix of this unit can be more appropriately considered as a secondary or subsidiary framework assemblage as it is almost identical mineralogically to the coarser framework quartz fraction. Chert is slightly more abundant, but the monocrystalline to polycrystalline quartz ratio is similar to that of the coarser quartz constituent. Overall, the framework and matrix quartz combine to make up greater than 90 percent of the total constituents. Aside from the finer grain size, averaging 0.03 mm diameter (medium silt), the matrix quartz is predominantly subangular and only moderately sorted (fig.14). Indeterminate cryptocrystalline clay is ubiquitous between the matrix quartz grains, and composes up to eight percent of the total constituents. Most of this material displays a yellowish green color under plane / - f :, ir Iai .' Z.Wt' 'vp, 4 I !t.. !' "-' ':;' ! f.t ?PV,'v polarized light, but is pseudoisotropic under crossed nicols. Hematite is common as a localized stain on the interstitial clays, but also occurs as large clots and/or as irregular, microns-thick bands and lenses. Some of these hematite-rich bands display a geometry or distribution which suggests the former presence of some type of bivalved animal, such as a pelecypod or brachiopod. These bands are characterized by a lack of quartz grains and a high proportion of clays and finely disseminated hematite. Their origin is unknown, but bioturbation, concentration by migrating pore fluids, or ultimate bioclast replacement are possibilities. In addition to the interstitial clays, most of the remaining original intergranular pore space is filled with euhedral, authigenic quartz crystals with characteristic pyramidal terminations; porosity and permeability are, therefore, very low (less than one percent). Additionally, a few subhedral authigenic quartz grains are present, which are surrounded by centrifugally-radiating, multiple growth rims. Very thin dustings of iron-stained clay outline the cessation of each period of overgrowth development. Dther grains lack the internal clay dust rims, but display well developed centrifugally-radiating overgrowths. The origin of the pc'es in which many of these must have originated is uncertain, but many may have been sites of broken biotic constituents leached out by pore waters undersaturated with respect to calcium carbonate. Calcite is rare to absent in this unit. Most of the matrix quartz grains are surrounded by optically continuous quartz overgrowths which cement the grains, while clay fills most of the remaining intergranular space, as previously mentioned The 70 coarser quartz grains, on the other hand, are characteristically lacking syntaxial quartz overgrowths or have only partial aver growths. Heavy minerals are present in trace amounts only, but include magnetite, zircon, apatite, epidote, brown hornblende (lamprobalite?), and indeterminate orthopyroxene. Magnet ite has largely altered to hematite and rare limonite. In contrast to the random bimodal quartz distribution in the lower unit, the upper unit is laminated and contains amore uniform range of quartz grain sizes. One set of laminae is characterized by angular to subrounded, coarse quartz silt in framework support, with subordinate to rare interstitial clay and hematite. Optically continuous quartz overgrowths occupy most of the intergranular space and cement the quartz grains, which are relatively equant to slightly elongate. Substantially more undulose monocrystalline and polycrystalline quartz is present than in the lower unit, but this may be a function of the finer overall grain size. Rare, extremely thin chlorite(?) fringes occur betweensome of the quartz grains, typically inhibiting overgrowth development; this clay coating is seldom found between overgrowths sharinga mutual contact. Large, scattered clots of hematite are common, rarely passing laterally into a diffuse network of iron-stained interstial clay and/or fine micas. The other set of laminae, whichare characteristically thinner, are finer grained, and contain appreciably more interstitial clay and hematite. Most of the angular to subangular, medium silt size quartz grains are monocrystalline and unstrained, in contrast to the 71 higher concentration of strained grains in the alternating laminae. In addition, there are fewer equidimensional grains andmore elongate or tabular grains. Syntaxial quartz overgrowths are common, as before, but most of the grains are entirely to predominantly surrounded by cryptocrystalline clays, possibly ofa chioritic affinity. X-ray diffraction analyses indicate that some of the interstial clay may be kaolinite, but in amounts only at the limit of detection of the diffractometer. Fine, scattered muscovite flakes are moderately common in the matrix; most are bent and deformed between the framework grains, but all display original parallelism with respect to the inferred depositional surface. In contrast to the alternating laminae, iron-staining is ubiquitous and typically more intense on the interstitial argillaceous material. Both sets of laminae contain a similar heavy mineral suite, including magnet ite, zircon, epidote, muscovite, and subordinate apatite, tourmaline, and hornblende. The hematite which stains the matrix was largely derived from the alteration of the detrital magnet ite and hornbjende. Most of the the heavies are subrounded, with the exception of the hornblende and muscovite, whichare subangular to angular. The transition between laminae is sharp, reflecting the abrupt decrease or increase of interstitial clay and the change in grain size and sphericity. Many of the laminae display a broad wavelength, low amplitude pinching and swelling habit, butare laterally continuous. The thinner, clay-rich laminae commonly tend to intersect or are abruptly deflected coincident witha rapid thickening of the lighter colored, clay-deficient laminae, creatinga 72 locally discontinuous character to the latter laminae. In outcrop, the laminated habit commonly grades laterally into a massive habit. Where thin, vertical fractures cross-cut the laminations, the laminae are not deflected, indicating that the fracturing event occurred after lithificat ion. These fractures are filled with mosaic and/or inwardly radiating sparry calcite, but all contain a thin hematite stain along the outer edge of the fracture wall, separating the calcite fill from the framework elements. This argues for the Introduction of iron-rich waters, which may have produced the iron stain on the interstitial clay, following and/ar during fracturing, but prior to deposition of the calcite fill. Blacktail Mountains The Kibbey Formation is more completely exposed on the north side of Sheep Creek Canyon, in the northern Blacktail Mountains. The 118.5 foot thick Kibbey section here is poorly exposed along a gentle slope which is transitional between the steeper slopes underlain by Lombard Limestone to the west, and the cliff-forming Mission Canyon Limestone on the east. Despite the poor exposure quality, two lithofacies can be discerned, a lower dolostone and an upper sandstone lithofacies (fig.15). The contact between the two lithofacies is arbitrarily taken at the base of the first exposed bed in which the quartz fraction exceeds 50 percent and is in framework support. The overall lithologic transition observed in the expose& Kibbey reflectsa gradual increase in calcite and quartz content, and grain size, at the expense of dolomite, which decreases proportionately. 73 KIBBEY FORMATION SHEEP CREEK CANYON (N V2INE I/41NW I/4)SECt 18)T. 9 S.,R. 8w.) LW .150' I I I SPARSELY rosslirERous IJACPZESTOHES D.,k yellowish brown; thin to .,ediui,bedded .chIn.id scuicles, di.srticvlated iso. i brachtopoda. ostracodu(?); baa. of t t Lor,b.rd I.inestone. c i i I I I I _jo. I _____-i C I - -. - QUARTZ ARCHITI. floderete yellowish brawn; -' ill loninstad (alternating vary fine sand and nodiwn sand lanai,..); eubroundad t. rounded quartz grains; calcite conented; SOX quartz. I z QUARTZ MACNIlE;Dark yellowish or.ng.; 7GX a fine sand; ubrouaded to rounded; noderetely S ...... well sorted; XIX dslonit.s nettled; pellets. -. .00LCPIITIC QUARTZMACMITE. Pale reddish brawn; a T SRI fine sands sub.ngul.r to subrounded; 0 f .,od.rat.ly well sorted; frenawerk support; lOX dolanate; vertical b.rrow.i not tied; w friable. C w SAJIRY DULOSTONC. P.1. yellowish brawn; 591 1..!. dolonita; porphyrotopto; 401 Quartz (very 4' fine sand); nettled; wispy; cloy scallops. SiLTY DOLOSTONC. Dark yellowish orange; 61x dolanite; porphyrotopic; 301 quartz (coars. silt); nettled. ______- SILTY COLOSTONC.Dark yellowish orange; sane a. next dolostona above. 0t.c.ntcrn*ty (''MUOSTONC.flediw, grey; lightly brecci.t.d; top .f A; sson Canyon Linestone. L 'Jo I I Lineetons cliffs I - I - U'- Figure 15. Kibbey Formation section in BlacktailMountains. Blank intervals represent cover. 74 Dolostone lithofacies. The dolostone ].ithofacies is best exposed in the lower 25 feet of the unit, and consists of laterally discontinuous, poorly exposed silty to sandy dolostone beds, which display a crude, thin- to predominantly medium-bedded habit. Tranching reveals a very non-resistant, chippy, limy siltstone and mudstone (Williams, Turner, and Gilbert, 1982) lithology between the poorly exposed dolostone beds. The upper 35 feet of this unit are covered by a grayish orange (10 YR 714) to yellowish orange (10 YR 7/2) soil with very fine to fine, silty dolostone and subordinate limy to dolomitic, quartz sandstone float. The lowest exposed bed crops out five feet above the uppermost Mission Canyon ledge. Re discussed earlier, the uppermost Mission Canyon paleosurface is irregular as a result of subaerial exposure and karst formation in Meramecian time. Quartz is the sole framework constituent, but makesup no more than 40 percent of the total constituents. Grain size variations are minor, but a crude, coarsening upward habit is present in the exposed lower half of the unit. The quartz in the lowest bed is predominantly subangularcoarse silt, which passes upward into subangular to subrounded very fine sand in the overlying beds. Sorting is moderate and sphericity is extremely variable. Most of the quartz grains are monocrystalline, although polycrystalline quartz and chert occur rarely. Finely crystalline, anhedral to subhedral dolomitecomposes at least 60 percent of the dolostone, completely surrounding and locally partially replacing the "floating" quartz grains. Subhedral 75 and rare euhedral dolomite porphyrotopes are scattered throughout the fine matrix, locally attaining coarse silt sizes. No evidence of rounding, which would suggest a detrital origin for these coarser dolomite rhombs, is recognized in thin section. X-ray diffraction reveals that the dolomite is slightly to moderately ferroan, and that calcite is in absentia or present in amounts too low to be detected. Variably rounded magnetite, zircon, tourmaline, epidote, and green hornblende grains make up less than one precent of the total constituents. Both the magnetite and hornblende are altering to hematite. Indeterminate clay is also admixed within the dolomitic matrix, but composes only a minor part of the matrix. Depositional textures have been obliterated by dolomitization of the original calcarenites. Mottling is ubiquitous throughout the exposed beds, but small clay scallops and wisps, approximately one-quarter inch long, are very common to the uppermost exposed bed. Petrographic examination reveals that these scallops and wisps consist chiefly of indeterminate hematite-stained clay, insoluble residues, and rare ruicrite and quartz silt grains. Pore fluid migration may partially account for these features, but the small size and random concavity, with respect to stratigraphic-up, suggest an origin resulting from bioturbation. The mottling is characterized by irregular patches with a greater concentration of dolomite, clay, and iron-oxides alternating with patches havinga lower dolomite to quartz ratio (approximately 3:2 or 3:1, versus 1:1or 12:1 in the adjacent mottles) and slightly less clay. No fossils or fossil fragments are present in the dolostone lithofacies. Fossils are very rare in the Kibbey Formation 76 throughout Montana, and specimens of meaningful biostratigraphic utility have not been reported to date. Sandstone lithofacies. Approximately half-way upsection in the Kibbey a second set of extremely subdued ledges crops out, separated by covered intervals of variable thickness (fig.15). The top of the unit is marked by a sharp, laterally continuous contact at the base of a thick sequence of thin- to thick-bedded, sparsely fossiliferous to fossiliferous wackestones. The uppermost 24 feet of this ljthofacies are covered. All of the covered intervals in this unit, however, are characterized by a grayish orange (10 YR 7/4) to moderate yellowish brown (10 YR 5/4) soil. Limy to dolomitic siltstone and fine grained sandstone float occur locally, but the rocks underlying the covered intervals are non-resistant and, therefore, unknown; the silty to sandy soil cover suggests the presence of poorly cemented siltstone or possibly very fine- to fine- grained sandstone. In outcrop the beds are predominantly massive and friable. Where bedding can be discerned, most is thin-bedded and planar. The uppermost exposed bed, in contrast, is very thinly bedded to laminated, displaying parting along slightly undulatory bedding planes. Grading is not recognized in any of the exposed beds of this lithofacies. As in the underlying lithofacies, fossils are absent in outcrop, although small vertical burrows, at least one inch long occur locally. The basal bed is very similar to the underlying dolostorie ns appreciably more quartz. The quartz 77 content in the exposed part of the sandstone lithofacies increases rapidly upsect ion, from 60 percent at the base to 90 percent in the uppermost exposed bed. Conversely, the amount of fine, mosaic dolomite, of subhedral to rarely euhedral dolomite rhombe, and of cryptocrystalline clay in the matrix decrease, passing upward into drusy calcite and subordinate dolomite. Mean grain size of the subangular to predominantly subroundedto rounded quartz grains is moderately variable, ranging fromcoarse silt to medium sand. Syntaxial overgrowths are common to the quartz grains, which average 0.19 mm in diameter (fine sand). few of the rounded framework grainsare obscured by a dense, dusty alteration product which is probably kaolinite,suggesting that the detrital grains may be orthoclaseor plagioclase; the absence of sericite argues for an orthoclase origin. Dolomitized pelloids and echinoid fragmentscompose five to six percent of the total constituents. Most of the pelloids are slightly elliptical, averaging 0.1mm in diameter, ar,d all display a thin, brown, micritic envelopeor peripheral film. Relatively coarse, centrifugally radiating pseudomorphic dolomite overgrowthspartially to completely surround the pelloids, terminatingabruptly against the framework elements and/or adjacentovergrewths, but developing a sawtooth termination where surrounded by thedirty, finely mosaic matrix dolomite. Where the pelloids are in direct contact with the quartz framework grains they are typically deformedor squashed. few of these structures appear to becollapsed ooliths, as the micritic rim is broken and locally overlaping. Syntaxial overgrowths are missing on these elements. Internal structures characteristic of ooliths are missing, but may have been destroyed by boring and complete micritization, and/or subsequent dolomitization. Conversely, these may have been rounded bioclasts witha thin, hardened micritic envelope which broke during depositionor subsequent compaction. Many of the larger, well rounded elements, averaging 0.2mm in diameter, are limpid to only slightly drusy, andmore coarsely crystalline, in contrast to the dirtier, cryptocrystalline pelloids. Optically continuous, limpid overgrowths are the ruleon these variably rounded grains. Many have a faint to pronounced, but thin, micritic or iron(?)-stained rim between the bioclast and overgrowth, which defines the rounded shape (fig.16). The replacement dolomite displays unit extinction, which suggest replacement of an overgrown monocrystalline calcite element, such as an echinoid plate. The absence of a lumen structure does not preclude the possibility that some of these fragmentsare ossicles, but does indicate that they were either broken and reworked (abraded) prior to deposition or are entirely platesor plate fragments. The matrix is almost exclusively dolomitic in the lower beds, although microspar occurs in trace amounts, primarilyas a rare cementing agent. porphyrotopic texture, of very fine sand size, subhedral dolomite rhombs "floating" ina matrix of medium to coarse silt size, subhedral to euhedral rhombs and/or mosaic dolomite, is very common. Cryptocrystalline material, which is yellowish to orangish brown under plane polarized light, locally 79 I 1MM Figure 16. Dolomitized bioclast (echinoid plate or ossicle fragment?) in dolomitic quartz arenite. Note thin iron(?) stain which defines the original shape of the abraded rnonocrystalline bioclast. Euhedral overgrowth is in optical continuity with bioclast. Kibbey Formation, unit 9, Sheep Creek Canyon section. Crossed nicols. surrounds or occurs between the matrix dolomite. The pseudoisotropic character under crossed nicols and very low relief suggest that this is clay. Small, intergranular pockets of this material locally make up approximately five percent of the rock. A crude laminated habit occurs locally in the lower part of the unit. The uppermost exposed bed, in contrast, is characterized by a laminated habit and rare dolomite (fig. 17). The dolomite occurs locally as small, welldveloped rhombs in the drusy microspar matrix and along the corroded margins of a few quartz grains. Monocrystalline quartz composes 83 percent of the rock, but chert is much more common than in the underlying beds, making up eight percent of the total constituents. Syntaxial quartz overgrowths are common, although many have been partially replaced or corroded by relatively limpid, low-magnesium calcite cement. Alternating, well sorted layers of subangular, very fine quartz sand and subrounded, medium quartz sand make up the millimeters-thick laminations observed in outcrop (fig.17). Larninae thicknesses involving the coarser grained Iaminae display much more variability than the finer-grained laminae, which are thinner overall. Many of the quartz grains in the finer grained laminae have low sphericity values and displaya crude to fair mutual orientation subparallel to bedding. Intergranular porosity is minimal, only one percent, and is restricted to the coarser-grained laminae. Small, irregular patches of relatively limpid poikilotopic calcite are also common in the coarser grained laminae. The engulfed quartz grains within these monacrystalline patches have ISP! -1mm-- FiQure 17. Plane laminated quartz arenite. See text for discussion. Kibbey Formation, unit 13, Sheep Creek Canyon section. Crossed nicols. been pushed apart, creating a local matrix support fabric, in obvious incongruence with the pervasive framework support fabric which characterizes this unit. Transitions between the laminae are very sharp, marked by the abrupt change in grain size previously rnent ioned. P common suite of heavy minerals occurs throughout the sandstone lithofacies. Magnetite and zircon are most abundant, locally composing one percent of the rock. Tourmaline is present in trace amounts. Many of the magnetite grains have partially altered to hematite, providing much of the iron for the locally intense hematite and limonite stain seen in the lower part of this 1 ithofacies. Deposit ional environment Introduction Kibbey sedimentation reflects initial eastward transgression of the Big Snowy sea into the Snowcrest and Big Snowy troughs following complete withdrawl of the Madisonsea from the area during early late to late middle Meramecian time. Despite the poor exposure of the Kibbey in the thesis area, several general conclusions can be drawn which point to depositionon a broad tidal flat along the advancing edge ofa shallow epeiric sea. Comparison of the Kibbey at Sheep Creek Canyon with Kibbey sections described elswhere in southwestern Montana support this explanation. The most obvious trend recognized in the Kibbey at Sheep Creek is that of a coarsening upwardsequence associated with a transition from dolomite-dominated to non-dolomitic, clastic-rich lithologies (fig. 15). As water depth of the encroaching sea increased, the Sheep Creek Canyon region passed froma muddy upper intertidal area to a sandy lower intertidal area, ultimately becoming completely submerged and changing froma clast ice-dominated system back toa carbonate-dominated system (plate 2). Recent studies of modern tidal flats ina variety of climatic settings have established several criteria for the recognitionof ancient tidal flats in the rock record. Modern tidal flats can be divided into three distinct environments:subtidal, intertidal, and supratidal. Recognition of all three environments is not always possible in the ancient record, however, becauseof multiple changes in sea level which removeor rework part of the record, and because of the inherent similaritiesbetween the deposit ional fabric of intertidal and supratidalenvironments. Tidal flats commonly develop along coastlines characterizedby moderate to high tidal rhythms, but with lowwave activity, in protected einbayments as estuaries, along epicontinentalseas, or behind protective barriers (Reineck and Singh, 1980;Shinn, 198!). Algal laminations, desiccation cracks,vuggy or birdseye porosity, low fauna! diversity and abundance,early dolomite, and a landward to seaward sediment distribution pattern,respectively, of mudflats, mixed flats.and sand f1atallai'atri thtidal flat eineck and Singh, 1980). Dolostone lithofacies The mottled, silty to sandy dolostones in the lower Kibbey represent deposition on an upper intertidal to lower supratidal environment. Rocks of the intertidal environment are typically difficult to distinguish from supratidal rocks; however,a few discrete differences can be utilized to differentiate thetwo. Algal laminations, desiccation cracks, fenestral porosity, and evaporites (or their pseudomorphic remnants)are considered as the chief criteria for recognition of the supratidal environment(Lucia, 1972). These features may also be found toa lesser extent in the intertidal environment, but this environment is commonly characterized by its bioturbated and burrowed fabric in the absence or near absence of algal stromatolites and evaporites. Burrowing, in contrast, is rare in the supratidal environment. Both environments are characterized by light colored sediments lackinga strong odor of decomposing organic matter (Shinn et al., 1969). The Kibbey dolostones are very finely crystalline, ubiquitously mottled, light in color, and lacka petroliferous odor. Sedimentary structures indicative of deposition ina supratidal environment are missing or rare. Park (1976) and Shinn (1983) have shown, however, that sedimentary structures in uncemented sediment which are diagnostic of the supratidal environment are reduced toa mottled texture as a result of burial, compaction,and dehydration. The numerous clay scallops and dark brown toblack, elongate wisps in the uppermost exposed dolostone bedmay reflect such processes; the scallops and wisps consist of cryptocrystallineclays, insoluble residues, and scarce quartz silt and micrite. Algal mats characteristically consist of such fine materials, trapped between the sticky, filamentous algal strands during storm and/orspring tides which transport the fine material high onto theupper reaches of the tidal flat (Davies, 1970; Park, 1976). Preservation of algal laminations is dependentupon several criteria, the most significant of whichare commonly adversely affected in the intertidal environment. Hubbard (1972) has reported on the role modern soft-bodied worms and boring algaecan play in the destruction of these organo-sedimentary structures. In addition, fluid loss during compactioncan account for a 70 to 80 percent volume decrease, reducing the formerlycentimeters-thick mat to a thin, often unrecognizable film oforganic matter and fine siliciclastic and carbonate constituents (Park, 1976). Thus, while the wispy, scalloped texture of theupper dolostone bed may be the result of burial processes, burrowingmay have also played a significant role in the partial destruction of thepotential algal laminations. Tysdal (1970) and Guthrie 11984) have bothreported algal stromatolites in the lower half of the Kibbey Formationin the Ruby and Bridger Ranges, approximately 25and 96 miles, respectively, east-northeast of Sheep CreekCanyon. Guthrie I984) also interpreted dolostone brecciasin the lower Kibbey as evidence of thin, laterally continuous evaporitedeposits which developed on a sabkha. Evidence of evaporites, suchas collapse breccias or anhydrite/gypsum pseudomorphs,are absent at Sheep Creek Canyon and in the Ruby Range, although thesedeposits may be represented by the covered intervals at eitherlocation (see plate 2). The Snowcrest trough area is believed to have been situated at approximately 4 N latitude throughout the upper Paleozoic (Opdyke and Runcorn, 1960; Sandberg et al., 1983), which would suggest the presence of a moist, tropical environment regionally. The lower Kibbey, however, is characterized by variably thick anhydrite deposits to the east, in the Big Snowy trough, suggesting a hot, semi-arid to arid climate (Harris, 1972; Ballard, 1969). Implied low-latitude paleotrade winds from the east to northeast during Paleozoic time CDpdyke and Runcorn, 1960), subaerial exposure of a great part of the Cordilleran platform during Kibbey time, and the elevated transcontinental arch to the east could have created a slightly drier regional climate than presently exists at these latitudes. A'silty to sandy do.lostone lithofacies is generally identifiable in the lower part of the Kibbey throughout the Snowcrest trough region (Plate 3). Primary and early dolomite is found on some modern tidal flats and is considered a diagnostic feature of such in ancient examples. The Kibbey dolostones consist of a very finely crystalline dolomite matrix containing several larger dolomite porphyrotopes. Porphyrotopic dolomite rhombs typically develop early in open pore spaces (Shinn, 1983); petrogrphic analysis indicates that the Kibbey porphyrotopes developed after dolomitization of the original mud, suggesting that both developed as syn- or early post-depositional diagenetic products. The original mud may have been pelletal, and this could account for scattered pore space in sediment which would not otherwise be expected to have much initial porosity. Dolomite concentrations in surfaceand near-surface sediments at Andros Island are foundto be intimately related to the position of the sediments relative tothe normal high tide level (Shinn at al.., 1969). Those sediments bearing the greatestamount of dolomite occur only a few inchesabove normal high tide level. A vertical relationship within thesediment is also noted; lithified sediment just below the unlithifiedsediment contains up to eighty percent dolomite, in contrastto the five to twenty percent figure reported in the latter. This relationship denotes the importance of early diagenetic dolomiteformation in the upper intertidal and lower supratidal environment(Shinn at al., 1969). Seepage ref lux in a semi-arid to aridenvironment is suggested as the predominant dolomite generating mechanismin these sediments. In contrast to the ref lux theory of Adamsand Rhodes (1960), which dependson increasing density of hypersalinebrines to displace connate waters in the slightly permeablecarbonates, studies of Holocene sabkhas suggest that the increasedhead associated with elevation of water on the supratidal flats duringstorms drives the ref lux system (Land, 1982). Because of the absence of evidenceof evaporite deposition on the upper tidalflat area the storm recharge-generated ref lux modelis favored in the thesisarea. Alternatively, a meteoric mixingmodel may be employed, as this dolomitization process willoperate in the absence of evaporites (Land, 1982). More time is required for thisprocess, however, which conflicts with the early diagenetic formation of the(ibbey dolomite suggested by theporphyrotopic microfabric. Many modern carbonate tidalflats are composed predominantly of fecal pellets and subordinate gastropods, foraminifera,or ostracodes (Lucia, 1972). Much of the diagnostic morphologyof the pellets is lost during compaction into bedding units (Howardand Reineck, 1972). As dolomitization increasesin these pelleted muds the pellets become progressively obscured, the dolomitecrystals ultimately replacing thepellets and acquiringa mosaic texture (Shinn et al., 1969). The high percentage of finelycrystalline, mosaic dolomite with scatteredporphyrotopes in the Mibbey dolostones, therefore, providesadditional evidence of deposition at or near normal high tide levelin an upper intertidal or lower supratidal mudflat environment. The absence of fossilsadditionally indicates deposition ina stressed environment inhibitoryto establishment and proliferation of a shelly fauna. These dolostones cannot- beconfused, therefore, with subtidal dolomites,which typically displaysome degree of preserved fossil material(Laporte, 1972). Finally, quartz silt andsand make up an appreciable amount of the Kibbey dolostones. This Is not surprising, however,as sand and silt are commonly found in mud flat sediments (Weimer,1982). Most of this clastic materialis transported via tidal channels onto the muddy, upper intertidalarea from the adjacent marine environment, lower shoreface,or sand flats by spring and/or storm tides (Bathurst, 197). In addition, some of theterriqenous constituent found in moderncarbonate tidal flats is wind-blown from nearby dunes or coastal spits (Purser and Seibold,197). An aeolian source may explainthe variable sizes of the detrital material found throughoutthe dolostones, although burrowing organisms and/or storm activityare also probably responsible for some of the observed mixing of grain sizes. case example illustrating the problemsinvolved with distinguishing intertidal rocksfrom supratidal rocks is found in the upper part of the Permian ClarkforkFormation in west-central Texas. These dolomites contain wispyto very poorly defined, irregular laminations,a few desiccation cracks, discrete quartz silt-rich beds, and ascarce fossil assemblageThe mottled dolomite is made up of a finelycrystalline ((5 microns) matrix with larger dolomite rhombs in the largerpores. The underlying intertidal rocks are thin to absent anddisplay ubiquitous mottling in addition to most of the characteristicelements of the supratidal rocks; recognition of two separatelithofacies reflective of different depositional environments,therefore, is also very difficult in this analog (Lucia, 1972). Recent work by Sando andothers (1985) has documented the occurrence of a conformably interveningcarbonate unit between the Mission Canyon Limestone andKibbey Formation in the Tendoy Mountains. Litholoqic features and paleontologicdata indicate that this unit, named the McKenzieCanyon Limestone, represents intertidal and supratidal deposition at the westernmost edge ofthe broad, post-Mission Canyonkarst plain (fig.9). The dolomitic unit recognized in the lower part ofthe Mibbey of the studyarea and elsewhere in southwesternMontana, therefore, may be correlative with the Mckenzie Canyonto the west., In conclusion, local textural and mineralogicalcharacteristics, regional correlation withother Kibbey sections (Plate 3),and stratigraphic position directlyabove a disconformity representative of pre-Kibbey subaerialexposure suggest that the dolostone lithofacies was depositedon a muddy, pelletedC?) upper intertidal to lower supratidal environment,peripheral to or within an esturine complex at the landward edgeof the advancing Big Snowy sea. Sandstone I ithofacies In contrast to the muddycharacter of the dolostone lithofacies, the overlyingsandstone lithofacies reflects deposition closer to normal low tide levelin a sand- and silt-dominated environment. Sand flats occur closest to thelow tide line and, therefore, are subjected forthe longest time to the strongestwave and current energy. Small scale current andwave ripple laminations are common,as are megaripples, and f laser and wavy beds, although bioturbat ionand burrowing commonly destroy the laminations and homogenize thesediment (Weimer et al., 1982; Shinn, 1983). Generally, bioturbation progressivelydecreases in overall significance withincreased sand content, related toa more seaward aspect across the flat. Upsection, these changes in sand content and associated sedimentarytextures are also observed in the sandstone lithofacies,reflecting gradual transgression of the Big Snowy sea and progressivelyseaward deposition in an esturine 1. ithotope. The lowest exposed bed belongingto the sandstone lithofacies probably reflects depositionin the mixed flat environment. This environment is characterizedby a variable admixture of bioturbated mud, silt, and sand (Reineckand Singh, 1S8). In contrast to the 91 underlying dolostone lithofacies,this lowermost sandstone bed contains more silt and sandthan mud (dolomite), but containsmore dolomite (mud) than the overlyingsandstones. Vertical burrows are common, suggesting a slightly stressedenvironment, yet the mottled texture indicates an abundanceof burrowing organisms, ruling out deposition in supratidal conditions. Dolomitized peloids and slightly to moderately abradedpelmatozoan debris indicate episodic flooding during storms which transportedsome subtidal elements onto the mixed flat. The slightly coarser andmore rhombic dolomite matrix, lacking the porphyrotopicdolomite rhombs found in theupper intertidal environment, alsosuggests deposition below normal high tide level. The textural and compositionalmaturity of the upper exposed sandstones is evidencedby the nearly monomineralic, subrounded to rounded frameworkassemblage lacking appreciable clay or mud, and displayingrelatively high sphericity values. The sandstones becomesandier upsect ion and ultimately display preservation ofprimary deposit ional structures. The uppermost exposed sandstone ischaracterized by thin, slightly undulatory laminations, incontrast to the mottled, unstructured sandstones exposed twenty feetlower in the section (fig. l). Small scale current and wave ripple laminations characterizesome sand flat deposits,as previously mentioned, although horizontal laminations and massive(bioturbated) fabrics are also commonly reported (Reineck, 1972; Weimerat al., 1982). Plane laminated sands, however, canoccur in many depositional subenvironments within a paralic setting, limiting the precision with whicha deposit ional environmentcan be determined given the minimal 92 exposure of the Kibbey in southwesternmostMontana. Plane laminated sands, for instance,characterize the intertidal foreshore beach, upper shoreface, andupper offshore (2 *m water depth) zones at Sapelo Island, Georgia, althoughthe upper offshore zone also displays variable degreesof bioturbation. In all of these zones wave energy is sufficiently strong toconstantly rework the sand, destroying most, if not all,biogenic structures. Conversely, the offshore zone containsa high density of burrowing species and individuals which almost continuouslyrework the sediment, resulting in interbedded plane laminatedand bioturbated sands (Howard and Reineck, 1972; Wunderlich, 1972). Lower intertidal sand flats (foreshore region of Howard andReineck, 1972) likewise contain many soft-bodied burrowing organisms whichdestroy deposit ional textures. The absence of bioturbat ion,lack of fossils, and preservation of planar laminations inthe uppermost exposed Kibbey sandstone can, therefore, be takento suggest deposition in an intertidal foreshore beach (lowersand flat) to possibly a lower shoreface environment, wherephysical reworking of the sediments by wave and tidal energy exceededbiogenic reworking. The source of sand during Kibbeydeposition is uncertain, but was probably derived from the elevatedtranscontinental arch to the east, the Canadian shield tothe northeast, and/or some unrecognized, elevated area to thenorth (fig. 6). During initial Kibbey deposition much of Montanawas subaerially exposed as lowland plains (Sando, 1976;Roberts, 1979). Thus, a some of the sand may have come from solutionand erosion of exposed upper Mission Canyon siltstones andsilty limestones. Brewster (1984) has noted that streams and rivers drainingthe area north of the Snowcrest trough during early Kibbeytime were silt- and sand-deficient. In contrast, tidal channels farthereast, in the Bridger Range, contain muchmore sand (Guthrie, 1984). A major part of the available sand,therefore, probably was transported westward through the Big Snowytrough into the Snowcrest trough. Harris (1972) has also noted that theinterrupted sandstone beds of the upper Kibbey inthe Big Snowy trough reflect the episodic derivation of sand fromthe craton during late Kibbey time; this episodic sand supplymay account for the notable paucity of sandstone beds and poor outcrophabit of the upper Kibbey in the thesis area. The yellow to red color ofthe sandstones and associated sandy to silty soil is impartedby the abundant hematite in the matrix of the rocks. A diagenetic origin for the hematiteseems to be the most tenable explanationfor its occurrence as it only locally stains therare matrix clays, but completely surrounds and obscures the detrital iron-oxideminerals (i.e. magnetite). The common mottled texture,predominantly fine sand-sized quartz grains, and absence ofripple laminae in the Kibbey sandstones in the thesisarea and throughout southwestern Montana may indicate lower than usualwave energy along the shoreline. A carbonate bank complex (ScottPeak Formation) began to develop and upbuild on the outercratonic platform coincident with initiation of Kibbey deposition(Stamm, 1984). This bank complex confined clastic sedimentationto the Snowcrest trough, restricting transport west into themiogeosyncline (Sando, 1976). With 94 continued upbuilding and/or slighttectonic elevation of the outer platform the bank may have partiallyattenuated some of the eastward-directed tidal andwave energy. The Snowcrest trough was relativelynarrow, probably having dimensions similar to the Red Seaor Gulf of California (plate 2), so wind-generated waves associated with thefetch of the trough were probably relatively small. Additionally, the shallow character of the basin and great distanceto the thesis area, approximately 100 miles landward of the inferredhinge line (shelf margin 111-1,2 of Sando, 1976), would alsoact to dissipate or reduce wave and tidal energy prior to arrival atthe sand flats (Shaw, 1964; Irwin, 196). Finally, an easterly to northeasterlypaleotrade wind could substantially diminish the potentialenergy of waves moving eastward (lartdward) by blowing thetops off the waves, destabilizing them and promotingpremature collapse prior to arrival at the shoreline (1. J. DeVries, personal communication, 198). It is very possible that, withthe exception of storm and spring tides, the breaker and surfzone was characterized by small swells, accompanied by small breaking waves. Sufficient wave energy must havebeen present, however, to transport sand-sized quartz grainsand winnow out much of the mud to medium silt-sized fraction. Most modern beaches consist chiefly of a medium sand-sized and/orcoarser grain fraction as a result of winnowing of the finer materialby high wave energy. The predominance of fine sand in thesandstone lithofacies, therefore, seems to suggest either a slightly lessenergetic shoreline regime, or the absence of a coarser sand supplyto this part of the basin, 95 or a combination of the two. The decreasing dolomitecontent and progressive increase in calcareous cement and matrixis also instructive. Normal tidal flooding of the sand flat must have been frequent enoughto inhibit dilution of the seawaterby meteoric freshwater which could ultimately generate dolomite. Flooding on the mixed flatwas less frequent, however, accountingfor the slow replacement of the pelletal mud with dolomite. The rare dolomite in the uppermost, laminated sandstone may have been transported from theupper intertidal or supratidal areas by strong, episodic winds,or developed as a late earlyto late diagenetic precipitate. The thin sandstonesequence exposed at Sawtooth Mountain can be correlated tentatively to the uppermost exposedsandstone bed at Sheep Creek Canyon,or is, at least, correlative to the middle to upper part of the sandstone lithofacieshere. The non-dolomitic, mottled to laminated, quartz arenite lithologyat Sawtooth Mountain isvery similar to the uppermost exposed sandstone bed at Sheep Creek Canyon. additionally, the upper part of the Kibbey Formation throughout southwestern Montanaconsists predominantly of sandstones withsubordinate dolostones, In contrast to the lower, dolostone-rich, sandstone-deficientsequence. The sandstones exposedat Sawtooth Mountaincrop out approximately 34 feet below the lowest Lombard outcrop,equating to a position well within the upper part ofthe Kibbey, which generally includes atleast the upper 6 feet of the formation (Plate 3). Thus, both lithological affinity and stratigraphicpcition 'I"' at Sawtooth Mountain is correlative with the sandstonelithofacies at Sheep Creek Canyon. In contrast, however,the Kibbey sandstone at Sawtooth Mountain is generally finergrained and contains more interstitial clay. Deposition of these sandsand silts may have occurred in quieter water, slightlyseaward of the sand fiat ina shallow, innermost shelf to lowermostshoreface environment. The finer grain size may also reflectdeposition higher on the tidal flat in the mixed fiat zone, butthe noteworthy absence of intergranular calcite or dolomite diminishes the viability of this option. Kuim and others (197!) have noted a similar fining seawardrelationship of terrigenous clasticmaterial along the modern Oregonand Washington shelf, associatedwith sorting and transport by longshot-c and tidalprocesses (mixing of unlithified Pleistocene shelf sands complicates thisrelationship, but the seaward fining trend involving modernclastics is present). Once deposited, these silty sands are quickly reworked by bottom dwellers (Kulm etal., 1975). A similar homogenizationprocess is envisioned here, although some of the bimodalcharacter may be the result of seaward transport of sandor silt grains by strong seaward directed breezes. Shamal winds in the modern PersianGulf are likewise reported to frequentlycarry sand and silt particles competely across the gulf (Shinn, 1973). The laminated upper part of the sandstone exposed at SawtoothMountain may reflect a short-term period of lowering ofwave base or seaward progradat ion of the tidal flat complex whichbrought the bottom sediments toa level near or above normal wave base. The absence of a recognizable £----- '- --nd flat and lowershoreface-innermost 97 shelf facies can be justified,in part, by the low waveenergy proposed earlier and by thenon-resistant character of the Kibbey Formation. This non-resistant characterprobably reflects the overall fine grain size of theKibbey in southwestern Montana. Siltetones and subordinatemudetones are commonly interbedded with the sandstones eastof the study area, explaining the infrequent outcrop habit there,and are probably common in this area as well (Plate 2). Little is known of Kibbeydeposition on the south side of the Snowcrest trough because offaulting and post-Lombard, pre-Amsden uplift and erosion (plate2). In the Bridger Rangearea, at the northeasternmost end of theSnowcrest trough, Guthrie (1984) recognizes supratidal Kibbeydeposits north and south of therange, peripheral to and transitional with intertidal deposits in thecentral part of the range whichare coincident with the paleotrough axis. The upper Kibbey unit thins significantly to the northand south, onto the late PaleozoicLombard arch and Wyoming platform, respectively, displaying a mirror image facies patternon either side of the subsiding trough axis, similar to thatseen in the lower Kibbey unit (Guthrie, 1984). Isopaching of the total Kibbey Formation displays appreciablethickening of the formation in the axial part of the Snowcresttrough, although the apparent thinning to the southeast is poorly constrained. Faulting has artificially thinned most of the sections along thesoutheastern margin of the trough, although thin, complete Kibbeysections are locally present at Baldy Mountain and the southwesternmostend of the Snowcrest Range (covered; see Plate 2). It is likely, therefore, that the Snoworest troughwas characterized by opposing tidal flat complexes which mergednear the center of the troughor were separated by a shallowsea throughout its length during lUbbey deposition. Thus, Kibbey deposition inthe Sawtooth Mountain area may have occurred on a northwest-facingtidal flat complex opposite a south-facing complexin the Sheep Creek Canyonarea, or occurred in a very shallow,clastic-dominated sea which separated the two complexes. Age and stratigraphicinterpretation Assignment of a preciseage to the Kibbey Formation in the thesis area and elsewhere in southwestern Montana is notpossible because of the near absenceof any biostratigraphically useful fossils above the base ofthe formation. Correlation to time equivalent units deposited to the west in the south-centralIdaho area, and bracketing by underlyingand overlying units of known age, however, impose relativelytight age constraints on the Kibbey Format ion. As discussed previously, the uppermost Mission Canyon inthe thesis area contains Vesiculophyllum sp. and Diphyohyllumsp., which are indicative of middle Osagean to late earlyMeramecian time (Sando and Bainber, 1979). West of the Snowcrest Range, in the Tendoy Mountains, Meramecian conodonts occur in thelower part of the Kibbey, and Canadihvllum, Clisiohvllum, and Faberophyllum are reportedin the lower part of the Lombard Limestone (Sando et al.,1985); these coralsare diagnostic of a late Meramecian (Coral Zone IV)age. A diverse, abundant coral fauna of Foraminifara Zone 12affinity also occurs in the Mckenzie Canyon Limestone which conformablyoverlies the Kibbey here (fig. 3). Foraminifera Zone 12/1.3 boundary faunawass additionally collected 330 feet below thetop of the Mckenzie Canyon (Sando et al., 198!). Based on paleontological data ofbracketing units, therefore, kibbey depositionis restricted to a period beginningno earlier than middle Meramecian(Foraminifera zone 1.3) time and ending no later than lateMeramecian (Foraminifera zone 14) time in the vicinity of thehingeline (Sando et al., 198!). Sando (1976) recognizesa diachronous character in the kibbey, suggesting that Kibbeydeposition may have started and ended in the thesisarea slightly later than is alluded to by biostratigraphic evidence in theTendoy Mountain area to the west. Fossils recovered from thelower mudstone lithofacies of the overlying Lombard Limestonein the thesis area, unfortunately, do not provide any usefulage constraints, so precise dating of the kibbey-Lombard and transitionis not possible. Corals and brachiopods in the next higher,fossiliferous wackestone/packstone lithofacies of the Lombard,however, are diagnostic of Coral Zone V (earliest to late Chesterian; W. J. Sando and J. 1.Dutro, Jr., written communication, 1925). Therefore, the lower part of the Lombard must have been deposited during approximately lateor latest Meramecian to earlyChesterian time, restricting kibbey deposition to late middleMeramecian to earliest late Meramecian time in the present SnowcrestRange area. In light of a diachronic model for kibbey and Lombarddeposition, these ages comply well with slightly olderages in the same units to the west. LiIi] The few mineralogical andlithological trends which can be drawn from the meager Kibbeyexposures at Sheep Creek Canyon indicate easterly shifting ofthe strandline, as outlined previously, although minor regressive eventswithin the overall trangressionare recognized elsewhere in theSnowcrest trough (l3uthrie, 1984). In the absence of a more completely exposed Kibbey section inthe thesis area, such strandlinefluctuations can only be supposed. The recognized trends at Sheep CreekCanyon may be fortuitous oreven misleading, although correlationwith other Kibbey sections suggest that the observed trendsare real (Plate 3). Construction of an isopachmap of the total Kibbey Formation in southwestern Montanaclearly illustrates thepresence of a subsiding basin normal to thecratonic margin during Kibbey deposition (Figs. 18 and 19). Several peculiar variations in Kibbey thickness are noted at thehead of the trough, although theseare believed to reflect variablesubsidence in this part of the trough (Suthrie, 1984). The anomalously thick Kibbeysection at Bell Canyon (242 feet)may also reflect greater local subsidence, although the location ofthis section within the leading edgeof the Overthrust belt, combined withits predominantly covered habit, suggest the possibility ofunrecognized fault thickening. Alternatively, the thick sectionmay reflect ponding of clastic material behind a slightlypositive carbonate bank complex (Scott Peak Formation). Some of the observed variationsthroughout the trough may additionally reflect differential sedimentationrates, or the variable paleotopographywhich probably existed prior to and during early Kibbey deposition. (I ) I I - -t Cf -- . , lt'1 .-.'.. U S I.SUSNSSS&T4 U .. UsaaIsITePa$ ...... 1. SUSSs- uv ISOPACH MAP OP THE KIBBEY I FORMATION IN SOUTHWESTERN MONTANA SaSTUSU 551.9 55sw*S SaSU N8$5s$4iSt$\ Sass P...? ss5s5*sUIfl$ IN APPSNS*J.. I MILlS N * I.a.., i. '.1 Figure 18. Isopach map of the Kibbey Formation in southwesternMontana. Contour interval is 50 feet. Figure by the author. U V N.G I SNOWY\ TROUGH,I. MU5."S .'- 1 ' if SullY Al$INT . !_____ S NIUS ,. 1 US 15 I IS IS 45 I_SS -' I. NS ISOPACH MAP OF THE KIBBEY LATEFORMATION MISSISSIPPIAN IN THE SNOWCREST TROUGH mLMaTus II5. 1 f ..l.__s " erosion.SnowcrestFinur ContourTrough. interval is 50 feet. 19. Tsonah man of th Darkened areas represent regions of post-Kibbey uplift and/or Kibhv Fnrmatirwi in th Figure by the author. Late Misiinnian N)I-. 103 The Kibbey zero-thickness edge illustrated on Figure 18 is largely the result of pre-Amsden uplift and erosion, rather than true stratigraphic termination. The shaded regions on Figure 19, however, depict post-Kibbey, pre-Amsden, uplift and/or erosion which resulted in direct juxtaposition on either truncated Kibbey or Mission Canyon units. Thus, the remaining unshaded, isopached areas display actual Kibbey thicknesses in the part of the Snowerest trough unaffected by pre-Amsden erosion prior to Lombard deposition. The presence of a southwest- to northeast-trending basin is still evident, although it is broader and the actual Kibbey deposit ional margins can only be guessed at (fig. 19). The diachronous nature of the Big Snowy Group is well documented in the Big Snowy trough (Harris, 1972), and has also been suggested in the Snowcrest trough region (Sando et al, 1975; Sando, 1976). West of the study area the Kibbey, interpreted to be entirely of middle Meramecian age, conformably overlies the early middle Meramecian Mckenzie Canyon Formation, which conformably overlies the Mission Canyon Limestone. In the thesis area, however, the Kibbey disconformably overlies the Mission Canyon, although the hiatus represented by this break is believed to be of short duration (approximately one foraminiferal zone in length; fig. 9). Farther east, at the western end of the Big Snowy trough, a similar Mission Canyon-Kibbey relationship is noted, but four or more foraminifera]. zones are missing across the contact (fig. 9; Sando et al., 1975). It is apparent, therefore, that basal Kibbey deposition was tirne-transgressive from west to east . The notion 104 that the increase in the length of the post-Mission Canyon, pre-Kibbey hiatus to the east is a result of progressively greater uplift and erosion in this direction can be discounted because of the presence of the Charles Formation. This uppermost Madison Group unit in the Big Snowy trough commonly directly underlies the Kibbey in the axis of the Big Snowy trough (Maughan, 1984). The variation in the length of the hiatus, therefore, reflects later initiation of Kibbey sedimentation to the east. The diachronous character of the Kibbey is also borne out by the two informally recognized units within the formation which display basinwide distribution and maintenance of nearly constant thickness proportions from southwest to northeast (Plate 2). In the absence of a diachronic model for Kibbey sedimentation, explanation of the lower unit would necessitate time-synchronous deposition of intertidal and supratidal sediments across a tidal flat complex extending more than one hundred miles landward (fig.19). Although the tidal range necessary to generate such deposition may not require anomalously large values, several other hydrologic parameters suggest the fallacy of such a model. For instance, assuming a hypothetically (and highly unlikely) horizontal tidal flat of the previously established dimensions, the rising water would have six hours to migrate approximately one hundred miles, requiring a flow velocity of 16 miles per hour! The ebb tide flow usually displays a greater velocity than that of the flood tide, suggesting an even greater returning flow velocity, across the flat. These values characterize higher velocity river flow much more than swash zone velocities. Such velocities should generate large 105 channels and/or rnegaripples and other cross-bedding structures, but none are recognized. In addition, flow velocities of this magnitude would be capable of eroding and transporting grains much larger than the silt to fine sand which characterizes the lower unit; but such are not found here (Plate 2). Deposition of the upper unit, and the sharp transition between the lower and upper units, would require an abrupt basinwide rise in sea level (or equal basinwide subsidence) and time-synchronous shoreface deposition across an equally broad zone. This also seems unlikely. Thus, the most tenable way toaccount for the stratigraphic character of the Kibbey subunits is to apply a diachronic model in which simultaneous deposition in several different environments occurs throughout the trough, reflect irg local water depth and/or position on the tidal flat complex. The proportional thickness ratios and sharp transition between the upper and lower units, therefore, reflects lateral (eastward) migration of the different facies coincident with the overall rise in sea level or epeirogenic downwarp during Kibbey time. Comparison of Kibbey and Lombard thickness values in complete sections throughout the Snowcrest trough additionally suggests a diachronous character to the Kibbey-Lombard sequence as a whole (Fig. 20). In this construction, the Kibbey is observed to thicken with respect to the Lombard toward the basin margins and to the northeast, toward the mouth of the trough. In contrast, the Lombard is thickest with respect to the Kibbey in the axial part of the basin and to the southwest, toward the mouth of the trough. NSLSN 1 t I BIG INOWY TROUGH I /I * / I /1 - - L1 6 / I I I I J'fffJ'f _.. I I I £ I I I . . . -.. - V' ))JJJJfl I / (L/K) ThICKNESS RATiOS IN LATE '\ !MISSISSIPPIAN SNOWCRESTTROUGII i N .. .: _' was 1. ...- I l, Figure 2G. Map illustrating Lombard Limestone to Kibbey Formation thickness I-. ratios in southwestern Montana. Figure by the author. 107 LOMS1RD LIMESTONE: DESCRIPTION Introduction The Lombard Limestone crops out sporadically throughout the Snowcrest Range, commonly developing small hills or knolls adjacent to the major peaks of the range that are characteristically underlain by resistant Pennsylvanian and Permian age rocks (figs. 3,4). The best Lombard exposures occur at Sliderock and Snowcrest Mountains, where the Lombard crops out in steep, treacherous cliffs, associated with faulting and/or Pleistocene glaciation. The most complete section, however, is found in the Sawtooth Mountain vicinity, although thin covered intervals obscure a few important relationships. Elsewhere in the range the Lombard is variably exposed in sections having a moderate to large percentage of covered intervals which chiefly occur in the lower part of the formation. The Kibbey-Lombard contact is typically obscured by float or soil cover, or is missing because of thrust faulting. The total thickness of the Lombard, therefore, is uncertain at most sections in the Snowcrest Range. Most Cretaceous through Tertiary thrusting in this area was localized along the transition zone between the incompetent Kibbey Formation and the competent Lombard Limestone. Only a minor amount of section, if arty,is believed to be missing from the exposed basal part of the Lombard, except at Sunset Peak where back-limb thrusting has substantially shortened the Lombard section. The Lombard thicknesses in the thesis area are interpreted as minimum values, but close to the original values. Two to four ma.jor lithofacies are recognized at most of the measured section locations. Where all four lithofacies can be discerned they include, in ascending stratigraphic order of predominant occurrence, a lime mudstone, fossiliferous wackestone-packstone, calcareous shale, and dolomitic lime mudstone lithofacies. This ascending lithofacies sequence is best illustrated at Sawtooth Mountain (plate 3). Intertonguing of the first two lithofacies, which comprise at least 80 percent of Lombard deposition, disrupts and complicates the overall stacked lithofacies arrangement. Correlation of the lithofacies in the thesis area reveals six northeastwar&thinning lime mudstone tongues which interdigitate with six southwestward-thinning fossiliferous wackestone-packstone tongues (plate 3). The upper part of the Lombard is characterized by calcareous shale, which directly overl ies the fossiliferous wackestone-packstone lithofacies throughout most of the Snowcrest Range, and a capping sequence of variably dolomitized lime mudstone. Exposure of the thinner, uppermost two lithofacies is restricted to only three locations, although covered intervals at this level combined with characteristic float suggest their presence elsewhere in the range. Overall Lombard deposition in the thesis area reflects progradational carbonate sedimentation in response to episodic differential subsidence in the southwestern part of the Late Mississippian Snowcrest trough and/or sea level fluctuations. The fossiliferous wackestone-packstone and lime mudstone lithofacies reflect deposition in shallow, moderate to high energy environments 109 nd deeper, quiet water environments, respectively. Shallow water eposition will refer to sedimentation at, or above, normal wave 'ase, whereas deep water deposition herein refers to sedirnentat ion below normal wave base, within or below the photic zone. It is important to note that the sharp lithofacies transitions suggested by the correlation lines on Plate 3 are actually gradational. The lines which define the lithofacies tongue are best approximations of the transition observed in the field, and are not taken to indicate an instantaneous change from one lithofacies to the next. Sporadic covered intervals and insufficient internal biostratigraphic control additionally preclude precise definition of the tongue dimensions, although faunal and textural dissimilarities between the two lower lithofacies permit refinement of the tongues as shown. The lime mudstone lithofacies tongues are labelled on Plate 3 with the letter "D" to reflect deep water deposition as previously defined. Those tongues representing the progradational fossiliferous wackestone-packstone lithofacies are labelled with the letter "9" to reflect shallow water deposition. For the purpose of discussion the tongues are identified from oldest to youngest by the Roman numerals I through VI, followed by the letter "fl" or "S" to indicate the respective lithofacies; the same identification scheme is utilized on Plate 3. 110 Lime mudstone lithofacies The lime mudstone lithofacies consists of medium- to thick-bedded, cherty limestones with thin- to medium-bedded silty limestone and silty, calcareous shale interbeds. Laterally continuous, barren to fossiliferous mudstones and sparsely fossiliferous wackestones are characteristic of the lower part of this unit everywhere in the range. At Sawtooth Mountain, where much of this lithofacies is exposed, the lowest beds appear to be almost barren in outcrop and pass upward into the common fossiliferous mudstones and sparsely fossiliferous wackestones. As a result of the intertanguing relationship with the fossiliferous wackestone-packstone lithofacies, this I ithofacies generally thickens overall to the southwest. The thickest uninterrupted section is 41 feet at Clover Divide. The adjacent sections at Red Rock River and Sawtooth Mountain are slightly thinner (315 and 355 feet thick, respectively). This major tongue branches northeastward into four separate, thinner tongues. Two additional, stratigraphically higher tongues originate farther to the southwest and only extend to the Sunset Peak area (plate 3). Sawtooth Mountain affords the most complete, accessible exposure of this interval in the southwestern half of the range; it is best exposed in the northeastern half of the range at Snowcrest Mountain. Discontinuous to continuous ledge-forming sequences are common, interrupted laterally and vertically by covered intervals which reflect underlying less resistant liraestones, silty lirnestones, 111 and/or calcareous shales. In steeper sections the discontinuously exposed ledges can be traced along strike for tens to hundreds of yards with little or no variation in lithology. At localities where the slope underlain by this lithofacies is gentle, the ledges are typically very subdued and trenching is often required to establish the relationships between beds. Many of the planar to slightly undulatory mudstone and wackestone ledges display a laminated to more commonly flaggy splitting habit. Massive beds occur locally, although the aforementioned splitting habit is frequently observed in laterally equivalent ledges. The transition between the limestone ledges and less resistant silty limestone and shale interbeds is typically sharp and slightly undulatory, but a gradual transition over several inches is noted at a few outcrops. Chert nodules are common, although the greatest number occur in the lower part of the lithofacies, in tongues ID through IVD. The grayish orange (10 YR 7/4) nodules vary from irregular to elliptical, but the majority display a well defined augen shape and attain dimensions of six inches by eight inches. Chert stringers, typically moderate yellowish brown (10 YR 5/4) to dark yellowish brown (10 YR 4/2) in color, are less common and occur chiefly in tongues lID and hID, at Sliderock and Snowcrest Mountains (plate 3). Most of the stringers are a few inches or less in width and locally reach fifteen feet in length. The limestones are characteristically dark, ranging from black (Ni), to olive black (5 Y 2/1), to grayish black (N2) on a fresh surface. A slight lightening in fresh surface color is noted upsect ion at a few locations, however, becoming dark gray (N3) to 112 medium dark gray (N4).Greater variation is seen on weathered surfaces, which vary from very pale orange (10 YR 8/2) and yellowish gray (5 Y 8/1) to the more common light gray (N7) and light olive gray (5 V 6/1). In the field many of the rocks of this lithofacies appear to be barren or very sparsely fossiliferous.Laminated intervals are moderately common, but are subordinate in proportion to the massive intervals.In thin section the barren appearance of these rocks is found to be a function of the fine size of the allocheroical constituents.Petrographic analysis reveals that four microfacies characterize the bulk of this lithofacies, and that several other unique rnicrofacies occur rarely.The four most common microfacies include fossilferous raicrites (typically spicule- and ostracode-rich), sparse spicular biomicrites, sparse biomicrites (sponge spicules less significant to absent), and sparse to packed biopelmicrites. Straight to broadly curved sponge spiculos (monactines and diactines) and ostracodes dominate the biotic fraction throughout most of the lithofacies (fig. 21).Typically subordinate, but locally significant fossils also include calcispheres, pelecypods, brachiopods, echinoid ossicles and plates, and gastropods.Phosphatic skeletal fragments, forarainifera, and pollen spores(") occur rarely. Bioclasts tend to compose approximately 30 percent of the total constituents, although a few beds containing up to 60 percent bioclasts also occur.The majority of the bioclasts do not exceed very fine sand size and are disarticulatod or broken. Whole specimens are commonly present, especially in the lower part of the lithofacies.Evidence of abrasion is absent, suggesting that these 113 particles were not transported far, were transported solely in suspension, or represent in situ development with minor reworking. Micrite is the chief matrix element, although neomorphism has largely altered the micrite to microspar (<30 microns) and less commonly to psuedospar (>30 microns). Dark, organic-rich clots and threads anastomose throughout the micritic matrix, imparting much of the dark color observed in these rocks (fig. 21). Geochemical analyses indicate a total organic carbon content in these limestones ranging from 0.19 to 1.10 percent of the total rock.The high organic content of the rocks is evident in the field by the strong to very strong petroliferous odor given off when struck by a hammer, and by the oily film observed locally on fracture surfaces. Sparry calcite is very rare to absent, typically occurring only as intraparticle fill in whole fossils (fig. 21). In general, the lower and upper parts of the thick lime mudstone interval in the major tongue of the Lombard at Red Rock River, Clover Divide, and Sawtooth Mountain are dominated by sparse biopelmicrite with subordinate laminated sparse biomicrite and fossiliferous (spicular) micrite interbeds.The biopelmicrites typicallycontainsubequal quantities of bioclasts and peloids, the remainder of the rock being composed of organic-rich rnicrite. Random orientation and distribution of the biotic constituents is prevalent, although peloidal units displaying fossils aligned subparallel to bedding occur rarely.In a few places the fossils are additionally clustered into a pod-like arrangement, surrounded by less fossiliferous biopelrnicrite or biornicrite. The peloids in the biopelmicrites are typically elliptical in thin 114 1/2mm I Figure 21. Typical sparse biomicrite of lime mudstcire lithcfacies. Note abundant sponge spicules and disarticulated ostracodes which are oriented parallel to bedding. Few articulated, sparry calcite-filled ostracodes. Unit 10, Sawtooth Mountain sectic'ri. Plane polarized light. 115 section and average 120 microns in diameter. Much of the peloidal texture has been lost because of reworking of the sediment, or micritization and subsequent disintegration of the pellets prior to lithification, and/or diaqenetic alteration, suggested by the relict pelletal texture observed in many of the bioraicrites. Sponge spicules and ostracodes comprise most of the lime mudstones as previously mentioned, although echinoid ossicles and plates, gastropods, and disarticulated bryozoan fragments occur locally.Microscopic examination reveals that many of the brachiopods have very thin valves, averaging 30 microns thick and randomly bored.Foraminifera and trilobite fragments occur rarely in the upper part of this thick interval, at a level approximately correlative to tongue Ills or the upper part of HID.Trace fossils, which are crescent shaped (approximately 1/2 inch in total length) and of very low relief, are found along bedding planes in the lower part of this interval at Clover Divide.These traces closely resemble Helmanthopsis grazing trails described by Miller and Knox (1985; p.84, and their figure S on Plate 1). The laminites are typically the least fossiliferous appearing rocks in outcrop.The laminae are predominantly planar and very thin ((1/16 inch) to thin ((1/8 inch), although undulatory laminae and laminae up to 1/2 thick inch occur rarely.In thin section, calcareous inonactiries and whole to disarticulated ostracodes are found throughout these fossiliferous micrites and sparse biomicrites, accompanied by random occurrences of many of the aforementioned biotic elements.Siliceous sponge spicules are less common. Most of the calcareous raonactines probably reflect primary diagenetic 116 replacement of siliceous spicules by mosaic, low-magnesium calcite, while the siliceous monactines may reflect secondary diagenesis of opaline sponge spicules initially altered to calcite (J.K. Rigby, personal communication, 1985). P marked size variation is noted between the two sets of spicules, however, suggesting different origins or preferential replacement. Size sorting in the laminites is characteristically poor, although the shape fabric imparted by the bioclasts is typically excellent. Thus, the laminations observed in outcrop are discovered in thin section to be, in part, a function of the preferred orientation of the bioclasts, and also the result of subtle variations in spicular packing density, bioclast size, and organic matter content. Burrows and evidence of bioturbation are lacking in the laminated intervals, although isolated structures suggestive of burrows or cylindrical pellets, similar to those created by Pleistocene crabs, are observed in the lower part of the lithofacies at Sawtooth Mountain (T.J. DeVries, personal communication, 1985). The lowest exposed beds at Sawtooth Mountain are very finely laminated ((0.5 mm thick) and contain onlya few (one percent) scattered calcareous and siliceous monactines, and disarticulated ostracode carapaces which lie parallel to the lamiraae. Pt Clover Divide, phosphatic pellets occur in a very thin laminated interval within a bioturbated fossiliferous micrite bed near the base of the section. X-ray diffraction analysis indicates that these pellets, which attain dimensions of 6.5mm by 3.9 mm, are fluorapatite. Pn authigenic origin for these pellets is suggested by their scalloped outline, although a thin film of iron 117 oxideC?) surrounds most of the pellet and is locally missing art the rounded positive (Thigh") areas of the pellet edge, indicating transportation prior to deposition. The degree of rounding of the pellets appears to be, in part, a function of the pellet size, as the smaller ones commonly are well rounded and surrounded by a thin iron-oxide film, while the larger pellets display a more variable profile. The internal fabric is that of isotropic, amorphous pel].oids which, unfortunately, blend together near the margins, obscuring the possible presence of truncation textures which might positively indicate a detrital origin. The well rounded habit and absence of the peripheral iron-oxide film on positive areas, however, suggests a detrital origin for these pellets. Included in this laminated interval are several moderately large, disarticulated and whole pélecypods and gastropods, suggesting deposition as a result of an episodic storm event followed by draping and infilling of the interparticle space with finely laminated micrite. Phosphatic material is moderately common throughout the lower Lombard, although the majority is believed to represent fish debris and/or conodont fragments. Pt the extreme northeast end of the Snowcrest Range, however, finely disseminated phosphatic material of unknown origin occurs in the lowermost exposed spicular biomicrite bed (tongue ID). The middle part of the major lime mudstone tongue consists primarily of sparse biomicrites, biomicrites, and less common fossiliferous raicrtes. With the exception of isolated laminated intervals, many of the beds in this part of the lithofacies are bioturbated arid/or burrowed. Patchy or swirled micrite, 118 accentuated by differential neomorphism is common and can frequently be recognized by the variable weathering texture in outcrop. Where bioturbation is not evident in outcrop it can nonetheless be recognized by the associated random orientation and distribution of the bioclasts, reflecting post-depositional mixing. Some of the beds lacking laminations contain a bioclast assemblage displaying alignment subparallel or parallel to bedding. Burrows are moderately common within discrete levels throughout the middle and upper parts of the section. Correlation of these burrowed intervals from section to section is not possible. Most of the burrows are horizontal to inclined, and vary from straight to hooked. Straight, vertical burrows are found locally, but the majority of these occur in the lower part of the unit. ll of the burrows observed in the field and in thin section are characteristically short and of very small diameter, suggesting construction by annelids or some other slender, soft-bodied animal (1. S. DeVries, personal communication, 1985). s above and below, sponge spicules and ostracodes are generally ubiquitous, although pelmatazoan and brachiopod debris becomes increasingly significant upsection. The bioclast content in the middle part of the thick interval increases from Red Rock River (averages 16 percent) to Sawtooth Mountain (averages 38 percent). Farther northeast in tongues ID,lID, hID, and IVD the fossil content tends to remain constant or decrease slightly. ngular quartz silt is present in most of the limestone beds of this lithofacies, although seldom in proportions exceeding three percent. Silt content in the silty limestone and shale interbeds is 119 slightly higher, averaging ten percent. The expected decrease in quartz silt from base to top of the lithofacies is not recognized anywhere in the thesis area. In contrast, the quartz silt distribution is found to be highly variable from bed to bed. One ten foot thick fossiliferous mudstone sequence, cropping out approximately two-thirds up the major lime mudstone tongue at Red Rock River, is very silty, containing 9 to 3 percent angular to subangular quartz silt (fig. 22; units 10 to 13; see appendix ). Despite the anomalously high clastic content of this interval ostracodes, sponge spicules, pelmatazoan fragments, broken brachiopods, arid gastropods are present, although in greatly reduced numbers (three to eight percent). In accordance with the variation observed within the entire lithofacies, this silty limestone sequence is directly overlain by a fossiliferous limestone with less than one percent quartz silt. Similar isolated, silty, fossiliferous limestone beds are found at the base and middle to upper middle parts of most of the measured sections, although the quartz content never exceeds twelve percent and is commonly below six percent. Correlation of silty and sandy intervals from southwest to northeast is not generally possible, although a few silty sections can be crudely correlated through the thesis area. Tongue ID Plate 3 illustrates six northeastward projecting lime mudstone tongues indicative of six major episodes of deepening of the sea in the thesis area. The basal tongue,ID, directly overlies the I I 1MM 1 Figure 22. Silty fossiliferous rnicrite in lime mudstorie lithofacies. Note scarce bioclasts. Slightly crushed foraminifer in upper part of photo. Quartz is predominantly coarse silt-sized. Unit 11,Red Rock River section. Crossed niccils. 121 Formatior, and is relatively thin, never exceeding 50 feet in thickness. Sponge spicules (monact ines) predominate, although whole and broken gastropods, and disarticulated echinoids are relatively common as a subordinate assemblage. articulated arid disart iculated ostracodes, disart iculated pelecypods, and conodont fragments are less common to rare. These basal beds are generally massive, but the bioclasts are typically oriented parallel to subparallel to bedding. The larger faunal elements, however, often display a random orientation. Horizontal to inclined burrows are moderately common. Many of the burrows display slightly different infilling material suggesting multiple periods of burrowing or differential neomorphism. Some of the allochems, especially the sponge spicu].es, have been replaced by phosphate. Fine, faint yellowish to golden colored patches of phosphatic(?) material are additionally disseminated throughout the micritic matrix. Chert is also replacing some of the allochems. Tongue lID Tongue lID is similar to tongue ID, although ostracodes tend to be more abundant and scarce brachiopod, fenestrate bryozoan, and foraminiferal debris are also present. Horizontal and, less frequently, inclined burrows are abundant throughout this tongue. Many of the burrows are hooked, however, rather than straight. Echinojd debris tends to be common in the lower and northeastern part of the tongue, but is nonetheless subordinate in abundance to the sponge spicules. Most of these sparse spicular biomicrites are moderately to extensively bioturbated and poorly sorted. 122 Tongue hID The next highest lime mudstone tongue, tongue hID, contrasts sharply with the lower two tongues. Although sponge spicules are omnipresent and succeded by echinoid, ostracode, brachiopod, arid pelecypod debris, the himestones are characteristically argillaceous to silty. In addition, mosaic to fine, subhedral to euhedral dolomite rhombs compose up to ten percent of the limestone. A 2-foot thick, laminated chert limestone sequence dominates the lower part of the tongue at Snowcrest Mountain, although this sequence was not recognized or is covered at Sliderock Mountain. This cliff-forming unit consists of four- to eight-inch thick barren(?) lime mudstones separated by one- to two-inch thick chert stringers which are laterally continuous on outcrop. Tongue IVD The fourth deepening event, represented by tongue IVD, was also characterized by moderate clastic input, greater overall than in any of the three previous deepening events reflected in tongues ID, lID, and hID. In the northeastern end of the Snowcrest Range medium silt- to very fine sand-sized, angular to subangular quartz grains compose from nine to sixteen percent of the total constituents in the lower half of the tongue. As much as six percent quartz silt is also found in the southwestern end of tongue at Hogback Mountain, immediately northeast of its incorporation into the major lime mudstone tongue. Farther southwest, at Sawtooth Mountain, the uppermost sparse spicular biomicrites, 123 correlative with this tongue, contain rio more than two percent quartz. Finely crystalline, subhedral to rarely euhedral, rhombic dolomite makes up one to ten percent of the silty lime mudstones at Snowcrest Mountain. Dolomite is absent or very rare in correlative exposed beds farther southwest. Fine pyrite masses are common at this level in several of the exposed beds northeast of Clover Divide. Much of the pyrite occurs in chambers of foraminifers or as a partial replacement product of sponge spicules, brachiopods, and ostracodes. In contrast to the paucity of gastropods in the lower lime mudstone lithofacies tongues, gastropods occur basinwide in this tongue and correlative beds to the southwest. The overall faunal diversity, however, is similar to that of the preceding lime mudstones. Tongue VD and VID Tongues VD and VID originate in the southwesternmost 'end of the thesis area and cannot be traced to the northeast beyond Sunset Peak. The faunal assemblages in both tongues are similar to those elsewhere in this lithofacies. Bioturbation is ubiquitous, but many of the elongate bioclasts display a moderate subparallelism to bedding. Burrows are less common. Tongue VID is relatively thick at Red Rock River, but thin at Clover Divide, suggesting contrasting sedimentation and/or subsidence rates which caused the shallow to deep water facies transition zone to remain relatively fixed in position. Unrecognized faulting may also account for this thickness variation. 124 Fossiliferous wackestone-packstone 1. ithofacies The fossiliferous wackestone-packstone lithofacies is the best exposed Lombard lithofacies throughout the Snowcrest Range. In contrast to the lime mudstone lithofacies, medium- to thick-bedded fossiliferous wackestones and thin- to thick-bedded packetones, accompanied by subordinate sparsely fossiliferous wackestones, fossiliferous mudstones, and isolated grainstones characterize this lithofacies. One lenticular limestone lithoclast conglomerate occurs at the top of this lithofacies at Sawtooth Mountain. Very thin- to rarely medium-bedded silty and shaly limestone interbeds are common, although the majority are. shaly and several contain moderate to very abundant brachiopod assemblages. Table 1(at the end of this chapter) outlines the most significant features which characterize and distinguish the lime mudstone and fossiliferous wackestone-packstone 1 ithofacies. A parallel, planar to slightly undulatory, flaggy to slabby splitting habit is observed in many of the wackestone and packstone beds. Gradational contacts between the fossiliferous beds and silty to shaly lime mudstone interbeds are rare; most are sharp, and planar to slightly undulatory. Undulatory contacts U2' relief) are also common and tend to be restricted to the base of the fossiliferous beds. Mud injection structures are present where lithostatic stress caused a soft lime mud layer to inject into a weak zone in the overlying fossiliferous limestone bed. Grading and laminated intervals within the wackestones and packstones are rare; laminae are generally restricted to the barren to fossiliferous 125 mudstone interbeds, although they are also uncommon in these beds. The packetones vary in thickness, but are typically thin- to medium-bedded, except in the uppermost part of the Lombard sections where several thick to very thick beds commonly occur. Most crop out as laterally discontinuous ledges, but some can be traced across an entire hillside with only minor breaks of cover. Dark olive gray (5 V 3/1), to olive gray (5 V 4/1), to brownish gray (5 YR 5/2) colors are typically observed on fresh surfaces. Upsection in this lithofacies the limestone become slightly lighter, commonly displaying a pale brown (5 YR 5/2) to medium gray (N5) color. Weathered surface colors are extremely variable, generally ranging from yellowish gray (5 V 8/1) to light gray (N7). In addition to the slightly lighter overall color than that of the rocks of the lime mudstone lithofacies, a lower total organic carbon content is suggested in these rocks by their weak to moderate petroliferous odor. Bioturbat ion and burrowing are evident in many of the beds by the presence of small worm tube moldsand casts, common random,orientation and distribution of tie biotic elements, and the rare mottled appearance on outcrop. Theburrows are horizontal to gently inclined, and typically straight. No vertical burrows were found. Inclined dendroid burrows, up to1.5 inches long, occur locally. Chert nodules and stringers are abundant along discrete horizons, but generally are rare. Many display a grayish orange color (10 YR 7/4), but dark yellowish brown (10 YR '+/2) varieties are also common. Most of the chert nodules are small and 126 irregular, in contrast to the well defined augen shape characteristic of the nodules in the lime rnudstone lithofacie. Chert stringers are lees common than nodules and seldom exceed four inches in thickness and fourteen inches in length. Six southwest-projecting tongues are recognized in the Snowcrest Range area (plate 3). The three oldest tongues (IS-IllS) pinch out in the Hogback Mountain-Sliderock Montain area. The three younger tongues (IVS-VIS) extend to the southwest edge of the thesis area, and beyond. These upper three tongues are part of a very thick fossiliferous wackestone-packstone lithofacies sequence which dominates the upper third to half of each Lombard section in the thesis area. This tongue breaks into the three younger tongues at positions progressively southwest of the termination point of tongue IllS. Microscopic analysis of this lithofacies reveals a diverse assemblage of microfacies dominated by sparse and packed biomicrites, biopelmicrites, biosparites, and biopelsparites. Many of these units are poorly washed and moderately sorted. The most significant and diagnostic contrast with respect to the lime mudstone lithofacies is the abundance of pelmatazoan and brachiopod debris and the virtual absence of sponge spicules (fig. 23). Ostracodes also display a marked decrease in abundance in these rocks. This littiofacjes contains a more diverse and abundant macrofaunal assemblage than does the lime mudstone lithofacies; this contrast of macrofossil- and microfossil-rich assemblages provides the main criterion for recognizing and separating thetwo 127 Figure 23. Photomicrograph of poorly washed echinoidal biornicrite. Note abundant rnacrofossils (echinoids, planispiral gastropods, pelecypods, brachiopods) and paucity of microfossils (sponge spicules, ostracodes). This is a common microfacies of the fossiliferous wackestone-packstone lithofacies. Unit 10, Sliderock Mountain. Plane polarized light. lithofacies in the field. Additional distinguishing criteria for the fossiliferous wackestone-packstone lithofacieswhich are useful in the field include: (1) the absence to rare occurrence of laminites, (2) generally improved size sortingof the bioclasts,(3) increase in abundance of interparticle and/or intraparticlesparry calcite, and (4) the more resistant outcropcharacter. Most of the transitions between the limemudstone and fossiliferous wackestone lithofaciesare gradual, although a few sharp changes do occur. As will be shown, many of the fossiliferous wackestone-packstone tonguescontain a variety of microfacies, suggesting local variationsin hydrodynamics associated with slight fluctuations in waterdepth, circulation, and/or sedimentation rate. Tongue IS Tongue IS is restricted to the northeasternend of the Snowcrest Range where it is exposednear the base of the Lombard at Sliderock and Snowcrest Mountains. Fossiliferous and sparsely fossiliferous wackestonescompose most of this tongue, although fossiliferous mudstonesoccur in places between the wackestone beds. The basal bed at SnowcrestMountain is a sorted biopeisparite, containg 60 and 10 percent bioclastsand peloids, respectively. Disarticulated echinoids; trepostome,encrusting, and fenestrate bryozoans; and micritized foraminiferamake up the ma.jority of the skeletal fraction. Sponge fragments (rare) and spicules, and disarticulated ostracodes and brachiopodsare subordinate. Sorting 129 is excellent, as most of the grainsare of coarse sand size (average diameter = 0.8 mm), and many of the grainsare oriented parallel to bedding. Micrite (eight precent) is subordinate tosparry calcite (19 percent> and occursas isolated interparticle patches, and as intraparticle fill in the bryozoans and ostracodes. 1dditionally, many of the bioclasts display micritic envelopes. Small, rounded intraclasts of sparse spicular biomicrite compositionoccur rarely, composing only three percent of the rock. Syntaxial overgrowths, originating from the numerous echinoid fragments,cement the bioclasts. To the southwest this basal unit grades intoa sparse echinoid biomicrite (sparsely fossiliferous wackestone). In addition to the abundant echinoid fragments, fenestrate andramose trepostome bryozoan debris, brachiopod fragments and spines,and trilobite fragments and spines are present. Pelmatazoan ossicles and plates make up approximately 20 percent of thetotal constituents, followed by calcareous sponge spicules (tenpercent) and the other elements previously mentioned (fivepercent). ll of the bioclasts display evidence of slight tomoderate abrasion. In addition, a bimodal size sorting is noted; theechinoid particles average 1.3 mm in diameter (very coarse sand size),while the surrounding elements occur as finely comminuted bioclastic debris. Peloids, up to 0.5 mm in diameter, are isolated andrare, making up less than three percent of the rock. The overlying beds are similar,sparse to packed biornicrites. Sponqe spiculeschiefly monactines. are common inmany of these te the faunal assemblage. Echinoids are 130 omnipresent, however, and commonly match or exceed the spicules in abundance, in contrast to the spicule and ostracode dominated rocks of the lime mudstone lithofacies. rticulated brachiopods, gastropods, and disarticulated and broken pelecypods are subordinate. Pelecypods are rare in the lower part of this tongue and peloids are less common above the lowermost beds. Several of the beds contain small chert nodulesor stringers and a few beds are silty. Most of the rocks also display some degree of bioturbation, although the fossils are commonly aligned subparallel to bedding. The tongue is best defined at its thinner southwest end, exposed at Sliderock Mountain, where it consists of 29 feet of fossiliferous and sparsely fossiliferous wackestones. The variable character of the rocks exposed in this tongue at Snowcrest Mountain may reflect rapid migration of lithosomes associated with the unstable nature of this end of the basin early in Lombard time, and with the very gentle slope of the basin floor. Tongue XIS This tongue displays a northeast-to-southwest distribution habit similar to tongue IS, but is thicker. The lack of exposures at this level at Hogback Mountain prohibit accurateprojection of this tongue beyond a position midway between Hogback and Sliderock Mountains. Fossiliferous inudstones are less cdrnmon than in tongue IS and sponge spicules are subordinate to rare in the wackestone beds. Sparse biomicrites (sparsely fossiliferouswackestones) and packed, 131 unsorted to sorted biomicrites and pelbiosparites dominate in this tongue. As in tongue IS, no packstone beds occur. Disarticulated and broken brachiopod valves and spines accompany echinoid ossicles and plates as the chief bioclastic constituents. The subordinate fauna consists of a diverse assemblage of gastropods, pelecypods, trilobites, and small, dissepimented horn corals. Bryozoans are rare, in contrast to their abundance in tongue IS, and consist of small fenestrate and trepostome fragments. Foranainifera occur locally. Sorting is characteristically poor to moderate. Evidence of bioturbat ion occurs in most of the rocks, and horizontal burrows are common. Inclined burrows are less abundant. Several of the sparse biomicrites contain productid and chonetid brachiopods, including Inflatia cf. obsoletus Easton and several large specimens of Chonetes sp. Thin, shaly limestone interbeds in these units also commonly bear a brachiopod-rich taxa containing numerous articulated and disarticulated, but unbroken, productid and chonetid brachiopods. These brachiopod-rich, sparse biomicrites are less common to the northeast, at Snowcrest Mountain, where fossiliferous wackestones (packed biomicrites and pelbiomicrites) are more abundant. The few pelbiosparites in this tongue contain a faunal assemblage similar to the sparse biomicrites. Trilobite fragments, however, displaying excellent preservation of the internal canaliculi structures, are also moderately abundant. Size sorting is good, but a crude bimodality based on sphericity is present. The more ioclasts display an average diameter of 0.37 mm (medium 132 sand size), while the more spherical elementsare only fine sand-sized (0.18 mm) on the average. Many of the grains are randomly oriented, display evidence of abrasion, and have micritic envelopes. Several elliptical to irregular, spicular micrite-filled patches are observed in thin section, suggesting burrowing and infiltration by overlying mud prior to complete lithification. Intraclasts are not present. The upper part of this tongue reflectsa gradual change in the depositional. environment as the shallow water-dominated rocks grade vertically intà deeper water rocks of tongue IllS. This change is manifest in the increasing abundance of fossiliferous lime mudstones and concomitant decrease in macrofossils. As in tongue IS, the dominate lithology suggests shallow waterdeposition (as previously defined), but the occurrence of fossiliferous lime inudstones suggest some degree of variability in the depositional environment leading to an episodic lateral migration of the lithofacies on a scale finer than that used to define the sixmajor tongues. Tongue IllS Fossiliferous packstones anda very thick grinstone characterize this tongue, which extends southwestto a position in the vicinity of Sawtooth Mountain andSunset Peak. This interval is covered in the overturned sectionmeasured at Sliderock Mountain, but is moderately to well exposedat Hoqback and Snowcrest Mountains. Contrary to the relatively gradational transitions between lithofacies noted elsewhere, thebase of tongue 133 IllS is sharp. Rbrupt shoaling in the Snowcrest Mountainarea is suggested by a 31 foot thick, cliff-forming, fossiliferousgrainstone sequence which directly overlies a 40 foot thick sectionof "barrens' to fossiliferous, slightly silty lime mudstones oftongue hID (Plate 3). Bioclasts in this massive, sorted biosparitevary from medium sand- to very coarse sand-sized; the majorityare coarse- to very coarse sand-sized (fig. 24). Quartz is absent and all of the allogenic material finer than 0.8 mm in diameterhas been removed by winnowing currents or sediment bypass. The fossil assemblage is similar to thatobserved in tongue hIS, although partial echinoid stemsoccur, and sponge spicules, pelecypods, and coral debrisare absent. Many of the disarticulated brachiopod valves are thin-walled and highly convolute (spiriferids?), but most are unbroken. Likewise, many of the other randomly oriented bioclats are disarticulatedand slightly to moderately abraded, but few are broken. Syntaxial calcite overgrowths from the numerous echinoid fragmentscement the bioclasts (fig. 24). Micrite is restrictedto the intraparticle spaces. Subordinate dolomite (less than ten percent), varyingfrom finely mosaic to moderatelycoarse subhedral rhombs, occurs at the center of many of the rnonocrystahlinespar-filled interparticle spaces, indicating post- or syncernentation precipitation. Micritic envelopes are rare and thinon the bioclasts, although the foraminiferal tests are completely micritized. Pt the southwestern end of the tongue,exposed at Hogback Mountain, the basal lithology consistsof a sequence of thin- to 134 ______1mm- t Figure 24. Photomicrograph of echinoid-bryozoan biosparite (grainstone) at the base of tongue IllS (unit 41), Snowcrest Mountain section. Black spaces in center and lower center are reduced interparticle pores. Crossed nicols. 135 medium-bedded, poorly washed biosparites and sparse biomicrites separated by thin shaly partings or interbeds. Foraminifera are abundant and brachiopods are common, but echinoid and fenestrate bryozoan debris is predominant. Many of the fenestrate fragments occur as short, whole frond portions, rather than finely comminuted fragments. Size sorting is poor and most of the fossils are randomly oriented, suggesting post-deposit ional reworking by bioturbating organisms. Seven feet above the lowermost fossil ferous wackestone, fenestral and trepostomous bryozoans predominate, supplemented by numerous foraminifera, echinoid and brachiopod fragments, and disarticulated ostracode carapaces. Small tabulate corals, Michelinia cf. meekana Girty, are also common (fig. 25). Micritic envelopes are rarely present on the bioclasts. Peloids and indeterminate rnicritic lumps, less than 300 microns in diameter, compose four percent of the total constituents. Fossiliferous mudstones are common throughout this tongue, interbedded with fossiliferous wackestones and packstones in the southwestern end and sparsely fosesiliferous wackestones in the northeastern part of the tongue in the thesis area. Many of the mudstones are spicule- and ostracode-rich, but contain many echinoid plates and ossicles, and disarticulated and broken brach iopod fragments. bove the basal grainstone at Snowcrest Mountain a series of alternating medium- and thick-bedded, sparse biomicrites, sparse spicular biomicrites, and sparse to packed spicule-ostracode biopelmicrites crop out. Laminations are generally absent and many of these beds display a swirled micrite texture and random 136 Figure 25. Representative specimen of the tabulate coral, Michelinia cf. M.. meekana Girty, which occurs throughout fossiliferous wackestone-packstone tongues IllS through VIS. Specimen in photo from unit 5, Sawtooth mountain section. 137 orientation and distribution of the bioclasts, indicative of bioturbat ion. Inclined and horizontal burrows are common throughout this lower section. Dendroid burrows are scarce. Echinoids and mollusks are common at all levels, but brachiopods are rare. Where brachiopods occur, several are commonly whole; produtid varieties tend to predominate, although spiriferids are also common. Bryozoans are generally rare to absent, except in the sparse spicular biomicrate directly overlying the grainstone and at discrete intervals higher up in the section. Most of the bryozoans are encrsting forms or fenestrata fragments. Gastropods are characteristically large; some are greater than one inch in diameter. Dolomite is commonly present in amounts less than two percent. The middle section of this tongue is covered at Hogback Mountain, but the upper part consists of a thin interval of fossiliferous mudstones and packstones. The mudstones contain a sparse assemblage of echinoid ossicles, disarticulated and broken brachiopods and pelecypods(?), and subordinately ostracodes. The packstones are sparse biomicrites (43 percent bioclasts) and packed biopelmicrites (58 percent allochems) with an echinoid- and pelecypod-rich faunal assemblage. few of the pelecypods are articulated. Disartjculated trilobites and ostracades are also common, in addition to the characteristic brachiopods and bryozoans which are less abundant. The bioclasts in the mudstones are typically oriented parallel or subparallel to bedding while those in the packstone beds are randomly oriented. These packstones do not display evidence of washing, as the 138 sparry calcite which is present (five percent) is generally restricted to the intraparticlespaces of the bioclasts, and the naicrite matrix is rich in organic material, accounting for the dark color andvery strong petroliferous odor of these rocks. Differential neomorphism of the micrite, probably associated with bioturbat ion, has locally created a patchy texture which is visible in thin section. Peloids in the biopelmicrites only account for ten percent of the total constituents, but bioturbat ion and burial may have destroyed much of the original pelletal texture. The micritic peloids, which range in size from 40 microns to 200 microns in diameter, are coalesced into isolated, bulbous to slightly ovoid lumps (grapestones?) cemented by fine to moderately crystalline spar. In other parts of the rock the peloids have neomorphosed to microsar and have vague boundaries, imparting a remnant peloidal textur4to the matrix. Tongues IVS-VIS: Introduction Tongues IVS, VS, and VIS branch from a major tongue whose thickness equals to exceeds that of tongues IS through IllS combined (plate 3). Barren and fossiliferous mudstones are less common than in tongues IS through IllS, however, and fossiliferous packstones are more abundant. Fossiliferous wackestones are ubiquitous and dominant throughout most of the major tongue. Sparsely fossiliferous wackestones are also moderatelycommon, but primarily occur at the extreme northeast and southwest end of the thesis area. At least two thin fossiliferous grainstone bedsoccur in the uppermost part of this principle tongue, anda limestone 139 lithoclast conglomerate caps the lithofacies at Sawtooth Mountain. Owing to the more resistant, ledge-forming character of the wackestones and packstones in this tongue, it can be easily recognized throughout the Snowcrest Range and provides a useful index interval for determination of relative position in the Lombard section. The majority of the small to moderate hills which are underlain by Lombard Limestone Are capped by the fossiliferous limestones of this principle tongue and the triad of related tongues (IVS-VIS) to the southwest. The three upper tongues originate between I4ogback Mountain and Sawtooth Mountain, and extend progressively farther to the southwest with decreasing age. These tongues are slightly thicker than the lower three tongues, although the subtle faunal and textural changes noted from the root to the end of the tongue in tongues IS through IllS are also characteristic of these upper tongues. That is, sea level fluctuations and associated lithotope migrations are recognized in the rock record of these tongues, but these are too fine to accurately resolve and correlate in this invest i gat ion. Tongues IVS-VIS: Lower part The lower one hundred feet of this principle tongue, correlative with tongue IVS on the basis of similar vertical variations in fauna and lithology, consists of fossiliferous and sparsely fossiliferous wackestones which pass into a thin capping sequence of fossiliferous wackestones and packstones. Subordinate, poorly exposed fossiliferous lime rnudstone beds crop out between 140 the wackestones and packstones. Sparsely fossiliferous wackestones, subordinate fossiliferous wackestones, and isolated fossiliferous mudstones characterize the lower part of this tongue at Snowerest Mountain. Echinoid and brachiopod debris, and whole foraminifers compose most of the bioclastic fraction, although ostracodes, bryozoans, andsponge spicules (rare) also occur in minor abundance. Articulated brachiopods occur are less common. A few of the beds are silty and dolomitic. Finely crystalline dolomite rhoebs locally compose up to twenty percent of thesparse biomicrites and display a distribution habit controlled by previous bioturbat ion. Most of the bioclasts are broken, but display only slight evidence ef abrasion. A few contain micritic envelopes, although the foraminifera are completely micritized. Textural inversion is evident as all of the bioclastic material finer than 0.2 mm in diameter (fine sand size) is absent, although micrite and microspar make up almost one-half of the total constituents. The swirled texture in the rnicrite and random orientation and distribution of the bioclasts, combined with the patchy dolomite distribution are diagnostic of bioturbation. To the southwest, the majority of the beds in thisone hundred foot thick interval aresparse to packed biomicrites and biopelmicrites. Peloids, ranging from 25 to 300 microns in diameter, compose up to 50 percent of the totalconstituents in the biopelmicrites (fig. 26). The peloids display two stylesof occurrence,(1) as separate bodies cemented by limpid, monocrystalline to coarsely crystallinesparry calcite, or (2) as 141 F1mm_ Figure 26. Photomicrograph of poorly washed biopelmicrite. Note limpid sparry calcite cementingpeloids in upper left part of photo and inside articulatedbrachiopod. Spar also filling zooecia of fenest'ate bryozoan fronds. Large, spherical brown objects in right half of photo are micrite-filledautopores of a ramose bryozoan fragment. Interpeloidal spar decreases in abundance outside of photomicrograph. Unit 30, Sliderock Mountain I section. Plane polarized light. 142 tightly packed peloids with moderatelycommon concavo-convex to irregulary deformed contact boundaries. Bioclasts compose up to 58 percent of the total constuituents in these beds and consist primarily of disarticulatedechinoids, brachiopods, foraminifera, corals, and trilobites. qrticulated and disarticulated ostracodes, pelecypods,sponge spicules, and conodonts occur rarely. Slightly abraded, dissepimented solitary rugose corals (SiDhonoahvlj4 sp.1) are common in the lower part of this interval at Hogback and Slidarock 4euntains. Endothyrid foraminifera composeup to fifteen percent of the rock and are the chief constituent ina few of the biomicrites (fig. 27). Most of the formainjfers are benthicor planktonic, although encrust ing varietiesare additionally present in a poorly washed biopeisparite near the top of this intervalat Sliderock Mountain. q two foot thick bed containingclosely packed orthotetacean brachiopods ina death assemblage immediately underlies this foraminifera-richsequence. Rhabdomesid and indeterminate dendroid trepostomous bryozoans are abundant and progressively increasein abundance upsection, ultimately deminating the faunal assemblagein the capping packstone beds. Fenestrate bryozoans are proportionately less abundant than the ramose forms. Bryozoans are less abundant at the Sliderock Mountain section thanat Hogback Mountain, yet compose an integral part of the bioclastic fraction there. Despite the variability in dominant fauna ineach bed, pelmatazoan- arid d biopelmicrites characterize this 143 I mm Figure 27. Photornicrograph of foraminiferal biornicrite in tongue IVS. Sparry calcite fills chambers of most foraminifers. Replacement chert acting as local intraparticle fill. Unit 34, Hogback Mountain section. Crossed nicols. 144 The uppermost packstone bed which defines the top of this interval at Sliderock Mountain isan unsorted biopeisparite which contains 47 percent bioclasts, 26 percent peloids, andseven percent intraclasts. All of the bioclasts are subrounded to well rounded and have micritic envelopes. Encrusting foramininfera are commonly found on ghosts of bioclasts which have been completely replaced by limpid sparry calcite andare recognizable only by their shape and micritic envelopes. The intraclasts are chiefly elongate, abraded fossiliferous wackestone fragments which have also been partially micritized. Microscopic examination of the poorly exposed fossiliferous lime mudstone interbeds reveals the paucity ofsponge spicules and abundance of echinoid ossicles and plates, and broken brachiopod valves. Articulated and broken ostracodes are also present, but generally in subordinate amounts. Sorting of the bioclagts is typically poor and most displatya moderate tQ good preferred orientation habit. In general, bioclasts increase in abundance upsection, although little evidence for increasing maturityor shoaling upsection is recognized in this lower interval. Most of the beds display moderate to excellent size sorting of the allochemicalconstituents; very few beds contain bioclastic material finer than 0.22mm (very fine sand) and many exclusively contain bioclastsgreater than 0.5 mm in diameter (medium sand size). The echinoid, brachiopod, and coral debris commonly exeed the otherbioclasts in size, often by at least one order of magnitude with respectto the Wentworth grain size scale. This bioclast size variationmay reflect variable source 145 areas for the individual taxa. Despite the good sorting noted in most of these rocks several of the beds contain fossil assemblages whichare oriented parallel or subparallel to bedding, and few of the bioclastsare abraded. Bioturbat ion and/or discrete burrows, however,are evident in most of the rocks, regardless of the degree ofpreferential orientation of the bioclasts. Patchy and/or swirled micrite textures, accentuated by differential neomorphism,are very common. Micrite typically exceeds sparry calcite as the matrix material, exceptin the isolated biopeisparite beds. Sparry calcite is common, however, filling the intraparticle spaces in chambered and articulatedbioclasts, and in random sheltered areas between bioclasts. Tongue IVS Fossiliferous wackestones at the base of Tongue IVSare in sharp contact with the underlying fossiliferous micritesand sparsely fossiliferous wackestones of the top of tongue hID. This contact is covered at most measured section sites, butis well exposed at Sawtooth Mountain where the contact issharp and undulatory. Where this contact is coveredor poorly exposed, the base of the tongue is taken at the abruptoccurrence of fossiliferous wackestones above the covered interval. The basal beds containa diverse and abundant macrofossil assemblage dominated by articulated and disarticulatedbrachiopods, including Spirifer cf. brazerianus Girty, and pelmatazoan plates and ossicles. Subordinate taxa throughout the basal part of this tongue include bryozoan, pelecypod, coral,ostracode, and 146 foraminifera debris, andrare sponge spicules. Peloids only account for eleven percent of the total constituents in the basal wackestones and decrease inabundance upsection. Many of the peloids are clustered, although the majority occur as isolated individuals; the peloids are typically cemented by limpid, mosaic to coarsely crystallinesparry calcite in both types of occurrences. five inch-thick storm layer containinga dense accumulation of broken and slightly abraded bioclasticdebris, oriented subparallel to bedding,occurs three feet above the base of this tongue at Sawtooth Mountain. The overlying fossiliferous wackestones contain fewerpeloids. Bryozoan fragments additionallyare very common, in contrast to their subordinate occurrence in the basalwackestones. Gastropods are present locally. Fossiliferous packstones (packed biomicrites and packed, poorly washed biosparites) characterizethe upper part of the tongue, except at HogbackMountain where sparsely fossiliferous wackestones bearinga similar faunal assemblage occur at this level. Disarticulated echinoid ossicles, plates, and partialstems are the chief constituents in thepackstones. Ramose bryozoans, brachiopods, gastropods, foraminifera, andpelecypods(?) are additionally present. Ostracodes, sponge spicules, and conodont fragments are absent. Peloids are also missing. Sparry calcite fills most of the intraparticlespaces, although no geopetal fill textures occur. s in the underlying wackestones, the bioclasts display rio preferred orientation. Differential neomorphism, creating irregular pockets and seams of pseudospar and/ormicrospar in the micrite 147 matrix, is ascribed to bioturbation prior to diagenesis. Very few of the bioclasts displayany evidence of abrasion. The upper contact with tongue VD is poorlydefined because of cover. Sparse spicular biomicrites, however,crop out within ten feet of the uppermost fossiliferous packstonebeds exposed at the top of tongue lyE, suggestinga potentially rapid shift in deposit ional environment. Tongues XVS-VIS: Upper part Fossiliferous wackestones and packstones, and subordinate fossiliferous grainstones, mudstones, and sparsely fossiliferous wackestones characterize theupper part of the major tongue, above the one hundred foot thick lower intervalpreviously described. The wackestone and packstone bedsvary in thickness, but tend to be thicker overall than in the lowertongues. The packetones display the greatest thickening upsection, however, as most are thin- to medium-bedded throughout thelower and middle parts of the tongue, but medium- to thick-beddedIn the upper part. Chert is rare to absent on outcrop. Fossiliferous wackestones predominate throughoutthe major tongue, as previously discussed, butpackstones equal to locally exceed the wackestones in abundance in theupper part of the tongue. This upper interval is largely covered atSnowcrest Mountain. The few beds which crop outare sparsely fossiliferous wackestones and subordinate fossiliferouswackestones.. Sponge spicules and ostracodesare rare in these beds. Pelraatazoan ossicles and plates, brachiopod fragments,and gastropods compose 148 most of the faunal assemblage. Sorting is poor to moderate, and very few of the fossils are oriented parallel to bedding. The wackestones which characterize thisinterval are chiefly sparse to packed biomicrites similar to those described in thelower interval. Isolated poorly washed biosparites are also present. The dominant faunal elements in thewackestones are the same as those in the lower wackestones, but gastropods,pelecypods, and less commonly ostracodes occur with greater frequency. Pelecypods are particularly common in the lower part of thisupper interval. Peloids are rare in the thin sectionsanalyzed throughout this interval, although a relict peloidal textureis present locally. Bryozoans are common throughout this intervalin all of the sections analyzed southwest of HoybackMountain. Northeast of this location bryozoans are abundantonly in the uppermost fossiliferous wackestones, andare typically subordinate to pelmatazoan and brachiopod debris inthe remainder of the interval. Ramose trepostome and cryptostome formsoccur with the greatest frequency (fig. 28). Indeterminate dendroid, trepostamous bryozoans occur at several levels inboth fossiliferous wackestone and packstone beds; mostare less than two to three millimeters in diameter and branch several times. The majority of the dendroid bryozoans are broken, but occuras articulated, branching forms up to 1.5 inches in length which lieparallel to bedding.. Fenestrate bryozoans are also commonly present, buttend to be concentrated in the uppermost wackestone bedsand in the packstone beds. Coralliferous debris is notcommon in most of the wackestones, hn1r'tw'1 4ficant portion of the faunal assemblage 149 I-i mm- Figure 28. Photomicrograph of bryozoan biornicrite. Note ntraparticle sparry calcite and local replacementby chert. Unit 39, Sawtooth Mountain section. Crossed nicols. 150 in the uppermost wackestone beds at Sliderock Mountain and in isolated beds elsewhere in the middle part of this interval. The corals which occur at Sliderock Mountain include Pmplexizaphrentis sp., Siphonophyllia sp., Vesiculophyllum sp., and indeterminate amplexoid corals. The occurrence of Vesiculophyllum sp.(fig. 29) suggests structural complications in the upper part of the Lombard here, as this coral seldom occurs in rocks younger than late middle Ileramecjan (Foraminifera Zone 13). Such complications were not recognized in the field, although some fault thickening, obscured by thin covered intervals, may have occurred here. The other corals present in this interval, however, are diagnostic of a Mississippian age; Sichonoohvllia sp. indicates that these rocks are Chesterian in age (Sando and Bamber, 1979; U. J. Sando, written communication, 1985). In addition to the corals, several brachiopods in this interval are also diagnostic of a Late Mississippian age (specifically Foraminifera Zones 16,17, and the lower part of 18; J. 1 Dutro, Jr., written communication, 1985). These brachiopods include Antipuatonia sp., nthracospirifer curvilateralis Easton, Composita sp., Composita cf. sulcata Weller, Diaphragmus cf. D. cestriensis Worthen, Flexaria sp., Inflatia sp., and Inflatia cf. LL.. obsoletus Easton (fig. 30). Evidence of bioturbation is highly variable from bed to bed, but some reworking of the fossiliferous lime muds prior to cementation is evident in most of the wackestones. Most of the beds display a swirled texture and/or differential neomorphism with a patchy habit. Burrows are moderately common, and tend to be 151 Figure 2. Specimen of Vesiculophyllum sp. from unit 11, Sliderock Mountain II section. Letter SO" is approKimately 2. mm in diameter. 152 Figure 30. Brachiopods collected in upper part of Lombard Limestone at Slider.-k Mountain (units 10 and 11, section II). Numbers in parentheses correspond to numbers in photograph. Inflatia cf. j obsoletus Easton (1, ) Composita ef.C. sulcata Weller (2) ntiguatonia sp.(3,4) nthracospirifer curvilateralis Easton (6, 10, 11, 12) Flexaria sp. (7) Inflatia sp. (8) iaphragmus cf.D. centstriensis Worthen (13) 153 horizontal to inclined; vertical burrows occur locally. Small, moderately rounded to predominantly angular phosphatic fragments are present in most of the wackestone analyzed in thin section. Many probably represent broken conodonts, although length and concavity of some of the fragments suggest an inarticulate brachiopod origin. Cochliodont fish teeth also occur locally (W.J. Sando, written communication, 198). Fossiliferous wackestones and mudstones are present in this interval at Sunset Peak. The Lombard section here is overturned and truncated by a back-limb thrust which has superposed Mission Canyon Limestone units over rocks of the upper part of the Lombard. The uppermost part of the Lombard section is covered and believed to be underlain by calcareous shale, fossiliferous wackestones, mudstones, and packstones similar to those found at this level at Sawtooth and Hogback Mountains. The uppermost fossiliferous wackestones and thin packstone interbeds which crop out at Sunset Peak are very different from those at the aforementioned locations. Many of these beds are very silty, containing up to 22 percent quartz silt and fine sand. Several carbonaceous flakes and fragments are additionallyseenon outcrop; microscopic examination reveals that these are wood() fragments with well preserved vascular structures (fig. 31). flark brown to black threads of organic matter anastomose throughout the niicritic matrix. Laminations are absent and the bioclasts are randomly oriented in most of the beds, suggesting bioturbation. Horizontal burrows are ubiquitous; in several places the fossils parallel the burrows, suggesting that the bioclastswere pushed aside during 154 1/2mm I Figure 31. Photomicrograph of wood(?) fragment in silty biomicrite. Unit 13, Lombard Limestone, Sunset Peak section. 155 excavation of the burrows. Pelraatazoan, brachiopod, pelecypod, and ostracode debris dominates thebioclastic assemblage. Gastropods, foraminifera, andsponge spicules occur rarely or are absent. Most of the faunal elementsare disarticulated or broken, but few are abraded, with the exceptionof some of the echinoid fragments. Stratigraphically below these wackestones and packstonesat Sunset Peak several fossiliferous mudstoneand sparsely fossiliferous wackestone beds crop out. The fossil assemblage in these rocks is similar to that in the wackestones,but sponge spicules are more abundant in some beds. Quartz is additionally less common, seldom exceed ing three percent. Both the wackestone and mudstone beds are rather anomalous when compared with laterallyequivalent units to the southwest and northeast. While the wackestones are believed to be autochthonous withrespect to the overlying Late Paleozoic rocks, the fossiliferousmudstones may be allochthonous. No evidence for a fault betweenthese two series of beds is recognized in the field, but unrecognizedthrusting along bedding planes may have occurred in thisarea. Fossiliferous packstone bedscrop out between the wackestones at several levels within thisupper interval. Thin to medium beds predominate, although these packstonebeds, in general, increase in thickness and lateral continuityupsection and to the southwest. The majority of the packstonesin this interval and the previously described lower intervalare laterally discontinuous in outcrop. Some of the beds whichcan be traced along strike pass into fossiliferous wackestone beds,reflecting a lateral change in the 156 abundance of bioclasts. In contrast to these thin to medium beds, the uppermost packstones are predominantly medium- to thick-bedded and massive, forming resistant ledges and isolated, thin cliff sequences. Very thick bedsoccur rarely.. The upper part of this interval is predominantly to completely covered at Clover Divide, Sunset Peak, and Snowcrest Mountain, although float typically denotes the presence of a covered wackastone and packstone lithology at this level. A few of the packstone beds consist of thin (inches thick) fossil-rich beds separated by less fossiliferous, micrite-rich partings or seams. Many of these very thin packstone layers containa different predominate faunal element than in the overlying and underlying thin layers. A constant diversity is generally recognized throughout the entire packetone bed, but the abundance of individual taxa in each sublayer commonly varies. Petrographic analysis reveals that the chief packstone microfacies are packed biomicrites and biosparites, poorly washed (packed) biomicrites and biosparites, and packed biopelraicrites. Echinoids, brachiopods, bryozoans, and corals commonly makeup the bulk of the packstones, althoughno one faunal element is ubiquitously dominant. Subordinate to locally abundant bioclasts include pelecypods, foraminifers, gastropods, trilobites, red(?)algae, orthoconic nautiloids, and indeterminate phosphatic skeletal fragments. Ostracodes and sponge spicules are characteristically rare to absent. Bioclasts typically exceed 40 percent of the total constituents. Peloids also occur locally, composing up to 26 percent of the rock. 157 Bryozoans increase in abundance upsect ion and dominate the bioclastic assemblge in the uppermost packstone beds. Rarnose trepostome (including rhabdomesids) and cryptostome varietiesoccur with the most frequency throughout most of this interval. Fenestrate bryozoans, though subordinate to uncommon in the lower parts of this interval, are commonly dominant in the uppermost packstone beds. Encrust ing bryozoans occur locally. Large solitary corals (Sihonoohvllia sp.; fig. 32), dissepimented rugose corals (Pmplexizaphrentis ep.), and tabulate corals (Michelinia cf. meekana Girty) are very abundant in the thick uppermost packstones and dipslope float at Sawtooth Mountain. Identical corals are present in similar packstone beds at the Red Rock River (tongue VIS) and Sliderock Mountain sections. diverse brachiopod assemblage, dominated by productid brachiopods, is also present in the packstones in this major tongue. In addition to the brachiopods previously mentioned from Sliderock Mountain and in the fossiliferous wackestones, ntiQuatonia cf. . aernodosa Easton and Inflatia cf.I. richardsi Girty are also present (fig. 33). Northeast of Sawtooth Mountain disarticulated echinoids and brachiopods predominate, and bryozoansare subordinate. The subordinate fuanal assemblage is similar to those to the southwest, but foraminifera and conodonts are absentor not recognized at Hogback Mountain. Thick packstone beds are missing or covered at Sliderock Mountain, although a series of thin, echinoid- and bryozoan-rich packstone beds crop out withina 35 foot thick 158 Figure 32. Solitary rugose coral,Siphonohyllja sp., fromupper part of Lombard Limestone (unit Zø, Sawtooth Mountainsection). Scale is in centimeters. 159 Figure 33. Brachiopods collected in units 13, 22, and 50, Lombard Limestone, Sawtooth Mountain section. Numbers in parentheses corrsepond to numbers of photograph. Spirifer cf. S. brazerianus Girty (1) nthracospirifer curvilateralis Easton (2, 4, 5, 7, 11) Pntiguatonia aff. . pernodosa Easton (3, 8, 9, 10, 12) Inflatia cf. I. richardsj Girty (6) 160 fossiliferous wackestone (sparse to packed biomicrite)sequence near the top of this interval. Bryozoans in these thin interbeds are chiefly fenestrates, cystoporids, and indeterminate raraose cryptostome(?) varieties (W.J. Sando, written communication, 1985). Peripheral boring and micritic envelope development is common in most of the allochemical constituents in all of theupper packstone beds and several of the lower beds in thisupper part of the major tongue. Bioturbation is ubiquitous as well, although some of the patchy spar texture in the micritic matrix is probably the result of weak to moderate washing by oscillating currentsor storm events. With the exception of the local trilobite fragments, very few of the bioclasts display evidence of extensive reworking and abrasion. Burrows are also common, varying from predominantly horizontal and inclined to less commonly vertical. Size sorting is generally moderate to good in all of the packstone beds,as bioclastic debris finer than approximately 0.25mm in diameter (fine sand) is commonly absent to rare. Stromatactoids are not recognized in the field or in thin section, nor do any of the aligned fossils displaya steeply inclined habit which distinguishes Waulsortian-type mud mounds. Many of the packstones crop out discontinuously andare difficult to trace laterally. In many outcrops, where lateral continuitycan be demonstrated, the packstone bedspass into wackestone beds and vice versa, sugqestingrapid, small scale variations inproductivity and/or the physical environment over short distances. The packstones in the lower part of thisupper interval and the lower 161 one hundred foot thick interval tend to be laterally discontinuous, suggesting a patchy distribution. The uppermost packstones, however, can be traced along strike for a considerable distance, suggesting a more widespread, sheet-likeC?) geometry. Cross-bedding and ripple textures are ubiquitously absentor not recognized in the packstone and wackestone beds throughout the Lombard in the study area. Tongues IVS-VIS: Uppermost part One washed packston (poorly washed oobiosparite) bed and two fossiliferous grainstone (sorted biosparite) bedscrop out stratigraphicall.y above the uppermost, thick-bedded packstoneson a dip slope at Sawtooth Mountain. The grainstones contain a moderately well sorted fattnal assemblage similar to the packstones. Elliptical peloids, averaging 700 microns in diameter are well preserved and commonly surrounded by the coarse, slightly dirty, syntaxial calcite cement which binds the a].locheinical constituents. Doliths are rare, composing one to two percent of the total constituents. Micrite is rare, occurring exclusively as intraparticle fill. Ooliths compose up to eight percent of the oobiosparite. Most are cored by foraminifors, displayan overlapping concentric and radiating cortical fabric, and havea slightly abraded, but unmicritized rim Cf ig. 34). Where the ooliths, which average 600 microns in diameter, are in contact with adjacent allochemsthe cortices are commonly deformed, indicating the soft, pliable character of the ooilith cortex during deposition. Rare, silty 162 I rJ° 1mm 4 Figure 34. Photomicrograph of sorted biosparite. Syntaxial calcite overgrowths cementing allochemical constituents. Note overlapping concentric and radiating cortical fabric and micritized forarninifer core. Unit 49, Sawtooth Mountain section. Plane polarized light. 163 micrite mud chips (angular intraclasts) are also present. The top of this major tongue and tongue VIS to the southwest is covered throughout the Snowcrest Range, except at Sawtooth Mountain where a thin, lenticular(?) limestone lithoclast conglomerate crops out beneath a limy shale sequence at the base of a large dip slope underlain by the uppermost packstones and grainstones (fig. 3). The predominant granule- to cobble-sized clast lithologies include unfossiliferous silty micrites, sparse biomicrites, packed biomicrites, unfossiliferous dismicrites, and rare fluorapatite pellets (fig. 36). ll of the lithoclasts are subraunded to rounded and display moderate to excellent sphericity. The subordinate matrix, composing only 20 percent of the total rock, consists of disarticulated, crushed, and commonly abraded bryozoans, brachiopods, echinoids, foraminifera, trilobites, and red algae(?) fragments in a micritic matrix (fig. 38). No preferred orientation is observed in either the matrix allochems or lithoclasts. Quartz silt to very fine quartz sand is typically minor, although quartz-rich (up to 20 percent) pockets occur locally. Most of the sparry calcite occurs as shelter and interparticle fill between the abraded clasts. Shelter, intraparticle, interparticle, fracture, and intercrystal porosity locally accounts for three to four percent of the total rock volume (visual estimate). Piercement features and concavo-convex contactsare locally present between adjacent clasts, suggesting that some of the clast were soft and deformable during deposition (figs. 35, 36). The uppermost contact of the fossiliferous wackestone-packstone lithofacies with the overlying calcareous 164 71 7: , 4 I Figure 3. Limestone lithoclast conglomerate exposed at base of dip slope on hill (9,566') just west of Sawtooth Mountain (unit53; U 1/4, SW 1/4, section 8, T.12 S., P. 5 W.). Note variable clast sizes and lithologies. 165 '1 Figure 36. Photornicrograph offiner fraction of limestone lithoclast conglomerate. Notevariety of carbonate lithologies represented by intraclasts andgranules, and variable degrees of rounding. Ramose trepostome byozoan fragment in matrix at right edge of photomicrograph. Unit53, Sawtooth Mountain section. Plane polarized light. 166 shale lithofacies is covered throughoutthe thesis area. The relatively thin covered interval, only eight feetthick, between the limestone lithoclast conglomerate and overlyingshales suggest that the transition is relatively sharp. A similar conclusion is drawn at Sliderock Mountain where a pronounced changein slope coincides directly with an abrupt change from shale andfossiliferous wackestone and packstone float to exclusivelyshale float above. Tongue VS Tongue VS is only exposed in the thesisarea at Clover Divide and Red Rock River. At the latter section interbedded fossiliferous rnudstones and packstonescrop out at the top of a 96 foot thick covered interval whichis underlain by dark gray (N3), barren to sparsely fossiliferous mudstone (basedon trenching); these interbedded rnudstones and packstonesare, therefore, taken as the base of this tongue. The lower packstones in this 84 footthick sequence are poorly washed biosparites containinga predominantly echinoid- and brachiopod-rich faunal assemblage. Echinoids outnumber brachiopods by two-to-one, and consistof a diverse collection of plates, ossicles, spines, and partialsterns. Broken fenestrate and cryptostome(?) bryozoans are alsocommon. Subordinate bioclasts include disarticulated ostracodes,whole gastropods, broken palecypods, foraminifera, conodontsor fish debris, and rare red (coralline?) algae fragments. Size sorting of the biciclasts is good and most are oriented subparallelto bedding. Little evidence of 167 abrasion is present and many are peripherally bored and micritized. Slight size variations occur across thin, irregular micrite--richseams which cut through the packetones. P vague pelletal texture is apparent throughout the micritic matrix, and small, irregular, micrite-rich intraclast are locally present. Isolated horizontal burrows also occur, but evidence of bioturbat ion is variable. The predominant, interbedded fossiliferous mudstones are spicular, in contrast to the packetones, but also contain abundant pelrnatazoan and brachiopod fragments, and articulated and disart iculated ostracodes. Fenestrate bryozoan fragments, foraminifera, and conodont fragments are also present. P few of these lime mudstone beds are also laminated, although the majority lack laminae and have a swirled (bioturbated) texture. To the northeast, at Clover Divide the packstonesare largely replaced by fossiliferous wackestones. In contrast to the abundant fossiliferous mudstenes at Red Rock River, however, fossiliferous wackestones outnumber these beds here. Tongue VIS This tongue is the southwestern extension of theupper half of the major tongue discribed previously. Fossiliferous wackestones and subordinate sparsely fossiliferous wackestonesare interbedded with fossiliferous lime mudstones throughout this tongue at Red Rock River. A 23 foot thick sequence of very resistant, thin- to thick-bedded, fossiliferous packstone ledgescrop out at the top of the tongue here. The wackestones consist exclusively ofsparse and packed biomicrites and biopelmicrites. No biosparites are recognized in this part of the tongue. s in the wackestones elsewhere in this lithofacies, echinoid and brachiopod debris is omnipresentand generally predominate. Fenestrate and subordinate ramose bryozoari fragments are also common in these beds. Additional faunal elements include ostracodes, pelecypods, gastropods,sponge spicules, and conodont fragments. Several Late Mississippian brachiapods and coralsoccur in the fossiliferous wackestones In the lower and middle part of this tongue. The corals, Sichonpohyllia sp. and Siohonophyllia excentrica Meek, are diagnostic of Sando Coral Zone V (Chesterian) deposition (W. J. Sando, written communication, 1985). The brachiopods are also diagnostic of Chesterian deposition (Foraminifera Zone 16,17, and lower part of 18); these include Chonetes ep., Ovatia cf. Qmuralis Easton, and Neospirifer praenuntius (3. T. Dutro, written communication,. 1985). Several specimens of the palecypod, Limipectin cf. otterensis Easton, also occur at the base of this tongue in a sparsely fossiliferous wackestone bed (identification by J. 1. Dutro, Jr., 1985). Many of the bioclasts are randomly oriented and distributed, scarcely abraded, and display partial to completemicritic envelopes. Size sorting of the bioclasts varies frompoor to good, although the more fossiliferous beds tend to bebetter sorted overall. Swirled micritic matrix textures, "dirty"sparry calcite patches, and/or differential neomorphismare present in the majority of the wackestone beds, suggesting reworkingof the sediment by an abundant benthic fauna. Burrows are less common 169 and are chiefly horizontal to inclined. The interbedded fossiliferous lime mudstones containmore sponge spicules and ostracodes than the wackestones, but also contain most of the biotic elements found in the latterbeds, as well. Size sorting is characteristically poor and most of the bioclasts are oriented either parallelor subparallel to bedding. The uppermost fossiliferous packstone beds (packed biomicrites) lack the sponge spicules found inthe wackestones, and contain a faunal assemblage dominated byramose trepostome bryozoans and subordinate fenestrate and cryptostomebryozoans (fig. 37). Unmicritized foraniinifers are very common also, in addition to the usual assortment of echinoid and brachiopoddebris. Encrusting bryozoans, which display excellentpreservation of the cystose (vascular) tissue,are also present (fig. 38). Isolated peloids occur locally, but compose no more than two percent of the rock. Several small specimens of Siphonohylliasp. occur in the uppermost packst one ledge. The upper part of this tongue consists ofapproximately 42 feet of cover which is underlain primarilyby barren(?), silty lime rnudstone. This covered intervalpasses vertically into a very thick covered interval characterized by yellowishorange (10 YR 7/6) soil and scattered sandstone float. The shale lithofacies which overlies this tongue elsewhere in the thesisarea is not present here, either as a result of a significant change in the depositionalenvironment in this area, or late- or post-Lombard,pre-Thisden uplift and erosion in this area. 170 F- Imm__I Fi;ure 37. Photornicrograpt, of packed biomicrite. Note abundant well preserved fenestrate bryozoan fronds and ramose trepostome bryozoans. Pbraded echinoid and brachiopod debris also common. Unit 109, Red Rock River section. Crossed nicols. 171 .1mm -4 Figure 38. Encrusting bryozoan on partially silicified, impurictate brachiopod valve. Unit 82, Red Rock River section. Crossed nicols. 172 Clover Meadow section thin series of cliffs crop out in thenorth-central Gravelly Range (SW 1/4, NE 1/4, section 16, T.9 S., R. 2 W.), 4hich previous workers have mappedas Mission Canyon Limestone or Amsden Formation (Hadley, 1969). Petrographic analysis and several coral collections, however, revealthat the rocks exposed in this cliff sequence are actually ofLombard Limestone affinity. The Lombard is exposed here, at CloverMeadow, as two thin cliff sequences which are herein attributed to recent; westward-directed gravity sliding along intra-Lombardplanes of failure (probably bedding planes) and/or along theKibbey-Lombard transition. The lower cliff and upper cliffsequences are separated by a gentle, hummocky slope, which displays evidence ofrecent movement, such as deeply cracked ground, and a few small, toppled andprecariously oriented trees. The total Lombard section exposed here is only 183.5 feet thick. Faulting associated with the gravity slidingrnay have removed some of the Lombard section locally, although theamount of dip separation represented by the hummockycovered interval between the two cliff exposures isunknown. Several discontinuous, massive, thick-bedded sucrosic dolomite bedscrop out near the top of the upper cliff sequence and are herein interpretedas the basal Conover Ranch Formation (fig.39). Several poorly exposed and thin-bedded siltstones and siltysandstones also crop out farther up the hill, above the basaldolomite beds. The lower cliff contains several coralliferous horizons andintervals which contain 173 Figure 39. Lombard Limestone exposed in west-facingupper cliffs a'c Clover Meadow,north-central Gravelly Range (SW 1/4, NE 1/4, section 16, 1. 9 S., R. 2 W.). Black line demarcates inferred Lombard Limestone (Ml)-ConoverRanch Formation (MPcr) contact. People near top of hill forscale (see circle). 174 Sihonophyllia sp. and Arnplexizaphrentissp., which are diagnostic of Coral Zone V (Chesterian) deposition (fig. 40). Most of the Sihonoohyllia sp. corals recovered hereare small, but the AmplexizaDhrentis sp. corals are typically large. The rocks exposed in both cliffs have a microscopic texture and faunal assemblage very similar to that found in the fossiliferous wackestone-packstone lithofacies of the Lombard in the Snowcrest Range. Owing to the thickness of this macrofossil-rjch wackestone and subordinate packstone interval, it is tentatively correlated to themajor fossiliferous wackestone-packstone tongue (IVS-VIS) in the Snowcrest Range. A more complete discussion of the faulting and inferred relationship of the cliffsequences can be found in Appendix A. The lower cliff sequence consists of massive, thick- tovery thick-bedded fossiliferous wackestones and packstones(sparse and packed biomicrites and biopelmicrites; fig. 41).Microscopic examination indicates that the chief faunal constituentsare disarticulated and broken echinoid and brachiopoddebris. Secondary taxa include fenestrate andramose bryozoans, foraminifers, solitary rugose corals, ostracodes,trilobites, arid sponge spicules. Sorting varies from poor to good, although the majority of the bioclastsare poorly to moderately sorted by size. Very few of the bioclasts displayany evidence of abrasion. Micritic envelopes occur locally. Most of the fossils are randomly oriented, but several intervals contain fossilswhich lie parallel or subparallel to bedding. Bioturbation is evident in most of the biomicrites and biopelmicrites. Discrete horizontal burrows are also 175 Figure 40. Two specimens of Sjphonophyllja sp. collected in Lombard Limestone in lower cliff ;equence (unit 4) at Clover Meadow, north-central Sravelly Range. Scale in centimeters. 176 FiQure 41. Lombard Limestone exposed in lower cliffs at Clover Meadow, northcentral Gravelly Range (SW 1/4, NE 1/4, section 16, 1. 9 S., R. 2 W.). Note massive, thick and very thick beds. Hammer in center of photograph for scale (see circle). 177 common. Three thick, sparsely fossiliferouswackestone beds crop out 23 feet above the base of thelower, cliff sequence, which contain abundant calcareoussponge spicules, foraminifers, and fenestrate and ramose trepostome bryozoandebris. The upper part of this cliff contains a series ofbiopelmicrites which consist of 25 percent bioclasts and 27 percent peloids. The bioclasts are locally clustered and in grain support, and muchof the micritic matrix has a local, relict pelletal texture whichsuggests reworking of the sediment by an abundant benthic epifauna and' infauna.. Very fine, scattered, subhedral dolomite rhombe localtycompose three percent of the rock. The upper cliffsequence consists of sparse biomicrites separated by an indeterminateinterval of doloinicrites and dolobiomicrites (fig. 39). The faunal assemblage is almostidenticle to that in the wackestones andpackstones in the lower cliff sequence, except that coralsare absent. Pelecypods, foraminifers, and trilobites are all locallyabundant, but tend to comprise the subordiante fraction of theassmblage in most of the beds. Peloids are rare, although micritization,extensive reworking by an active benthic infauna, and/or burialprocesses may have destroyed these allochems. Peripheral to complete micritizationof the bioclasts is additionally very common in thelowermost fossiliferous wackestones (sparse biomicrites). The lower-middle part of thisupper cliff sequence is dolomitic. Finely crystalline, mosaicto subhedral rhombic dolomite composes up to 30 percent of the totalconstituents, locally making 178 up 7t percent in a thin dolomicrite at the top of this dolomitic interval. Most of the rhombs are limpid, but a feware zoned, suggesting multiple growth episodes. Some additionally exhibit a calcite nucleus. Fine to coarse silt accounts for approximately five percent of the rock, but rapidly increases in abundance to ten percent of the total constituents in the capping dolomicritebeds. In contrast to the underlying and overlying beds,bryozoans are rare to absent in the dolomitic interval and ostracodes aremore abundant. Isoloated, scarce sponge spicules are the only bioclastic element in the dolomicrite beds. Most of the bioclast in the beds exposed in theupper cliff sequence are unabraded and randomly oriented, horizontal burrows are present, but most have been obliterated by excessive bioturbat ion which has generateda swirled, patchy, and/or monotonous reworked texture throughout the rocks. The uppermost beds are deeply weathered,sparse biomicrites containing a predominately silicified bioclast assemblage ofpelmatazoari and brachiopod fragments, and subordinatesponge spicules, ostracodes, pelecypods, and gastropods. Quartz siltis minor, composing only two percent of the total constituents. Phosphatic pellets locally make up four percent of the totalconstituents in these uppermost beds. Unlike the rounded phosphatic pellets foundat discrete levels within the Lombard to thewest, however, the irregular and locally diffuse edges on these pelletssuggest an authigenic origin. The. contact with the overlying, white, ucrosic Conover Ranch dolostones is covered by talus and/ordense vegetation, but appears to be sharp (fig. 39). No angular or undulatory relationshipsare 179 recognized, although the sharp lithologic change suggeststhe presence of a disconformity or a rapid change in depositional environment. Summary ll six fossiliferous wackestone-packetonelithofacies tongues which can be recognized in the studyarea display similar faunal and textural characteristics which distinguishthem from the alternating lime raudstone lithofacies tongues;these criteria are listed on Table 1, whichcompares and contrasts the two lithofacies. Several major lateral and vertical trendsare recognized within this Lombard lithofacies,however, which overprint the variations present in the individualtongues and correlative units in the major tongue to the northeast. These trends include the: (1) increase in abundance of packstones upsection and to the southwest,(2) increase in thickness and lateral continuity of the packstone bedsupsection,(3) rapidly decreasing abundance of sponge spicules,(4) increase in abundance of bryozoans to a position of dominancein the fauna! assemblage both to the southwest and upsect ion, and(5) the increase in abundance of deposits indicative ofvery shallow and/or agitated water conditions upsect ion. Lith facies Daracteristjc Fossiliferous Lie. .udston. wackeston.-packstone Major 1 ithofaci.s Barren to fossi 1 if.rous Fossi 1iferous wackeston., (Dura., 1962) 1 i.t eudeton., sparsely feesi 1 iferous packstone, fossiliferous wackst on. fossiliferous grainst one Major sicrofaciesFossiliferousuicrit., Sparse/packed biowicrit., (Folk, 1962) sparse biosicrite, packed biopeleicrite and sparse biopeleicrit. biopeisparit., packed biosparit. Major taxa Sponge spicules, Echinoids, brachiopods, ostracods bryazoans Minor ta*a Pelacypods, gastropeds, Forasinifera, corals, schinoids, brachiopods, trilobites, gastropods, ca1ciser.s, eonodonts naut iloids, ostracodes, conodonts, algae, sponge spicoles Lasinites Moderately coon Rare to absent Rioturbat ion Ioon Very cn Burrows All orientations; sost Horizontal to inclined; horizontal to inclined ieee dendroid Peloids Locally abundant Locally abundant Ooliths ASes* Rare to scarce B*oclastsz Size sorting Pàor Poor to excellent Orientation Variable; .any parallel Rando. to bedding Abrasion Absent Absent to cen Micritic Rare to absent Moderately con envelopes Color (fresh) Blk to grayish black Dark olive gray to brownish gray Chert nodules Coon Rare; locally abundant and stringers Petrol iferous Strong to very strong Weak to strong odor Table 1. Textural and faunal tharateristics of lime mudstone and fossiliferous wackestone-packstone 1 ithofacies. 181 Calcareous shale lithofacies The calcareous shale lithofacies is persistent throughout most of the Snowcrest Range. it is particularly well exposed at Sawtooth, Hogback, and Sliderock Mountains, where thicknesses of 42, 77, and 55 feet, respectively, crop outas ledges and cliffs. Elsewhere in the range this lithofacies is covered, forming gentle to moderate, grassy slopes. Fine shale float can typically be found in the dark colored soil on the grassy slopes, suggestingan underlying shale lithology. On the west and northwest sides of Sawtooth Mountain this unit can be traced for almostone mile, and discontinuous ledges of shale can be found along the entire east flank of Sliderock Mountain. The cliff-forming habit of these limy shales is restricted to the uppermost part of the unit, exposedon the north side of Sawtooth Mountain. This passes downward and laterally (to the southwest) into thediscontinuous ledges which typify this lithofacies throughout the remainder of therange (fig. 42). The fissile habit of these black (Ni) to olive black (5 V 2/1), silty, calcareous shalesvaries laterally, passing both vertically and laterally into a planar to slightly undulatory, laminated to flaggy habit. The entire unit characteristically weathers to a light gray (N7) to yellowishgray (5 V 8/1) color. Very thin to medium bedding is suggestedby abrupt vertical variations in splitting habit, and where thefissile splitting habit is absent these rocks are more correctlyclassified as silty lime mudstones (Dunham, 1962). Laminations are absent in most of the 182 Figure 42. Calcareous shale outcrop in large gully at baseof dip slope of hill (9,566') west of Sawtooth Mountain (W 1/2, SW 1/4, section 8, T. 12 S., R. 5 W.). 183 shale sequence at Sliderock Mountain, butare common in exposures to the southwest. Laminae vary in thickness from 3/32 inch (thin) to 7/16 inch (thick), averaging 3/16 inch thick,and are predominantly planar. Locally, individual lamina and/or sets of laminae are slightly undulatory to disrupted, displayinga pinching and swelling habit; features similar to flame structuresare rarely found in the laminated to flaggy beds. Many laminae are characterized by faint variations in coloron the weathered surface, possibly in response to the variable amount of preserved organic matter in the individual lamina. The predominantly fissile splitting habit of this unit, the common laminated character of the non-fissile mudetone intervals, and the relatively high proportion of organic material (incicated by thevery strong petroliferous odor), combined with the noteworthy absence of burrows and/or ichnofossils along splitting and bedding planes,are indicative of anoxic conditions, in the depositional basin, at least in the lower part of the water column. lthough these rocks appear monotonous in outcrop throughout the range, petrographic analysis revealsa subtle, diverse character which overprints the major mineralogical similarities. Micrite is the chief constituent of the rock, accounting foran average of 68 percent of the total constituents. Porphyroid rieornorphism has locally generated microspar and less commonly psuedospar. Organic matter occurs as a golden yellow to brown stain within themicrite and microspar matrix. In addition, irregular clots and dark brown to black threads anastornose throughout the microfabric. Short, black, horizontally stretched, sigmoidal wispsare also common. In 184 contrast to the Sawtooth and Hogback Mountainshales, those at Sliderock Mountain are found to containappreciably more visible organic matter and/or residue (asa dark stain) (fig. 43). Geochemical analyses reveala slightly higher total organic carbon content (by weight percent) in thecalcareous shales at Sawtooth Mountain than at Hogback Mountain;no data is available from Sliderock Mountain (see Appendix C). Simple, straight to very slightly curved,calcareous and subordinate siliceous sponge spicules(monaxons) are present in all of the shale samples analyzed. Calcareous sponge spicules are the only allochems found in the shalesat Sawtooth and Sliderock Mountains. A few disarticulated and broken inarticulatebrachiopod valves, and broken, recrystallizedpalecypod(?) valves are also present, however, at Hogback Mountain. No evidence of abrasion is found on any of the bioclasts. An increase in the percentage of allochemical constituents is noted fromthe southwestern end of the Snowcrest Range to the northern end,as bioclasts make up less than percent of the rock at Sawtooth and HogbackMountains, in contrast to 30 percent at SliderockMountain. In all sections the bioclasts are oriented parallel tobedding. Quartzose silt and subordinate clays makeup the terrigenaus fraction of the shale. Monocrystalline quartz dominates over chert, and polycrystalline quartz is absent. Grain size (nominal diameter) varies from 0.01 mm (fine silt)to 0.1 mm (very fine sand), averaging 0.03 mm (coarse silt) at SawtoothMountain. Slightly finer average grain sizes, 0.028mm and 0.02mm, respectively, occur at Hogback and Sliderock Mountains,and the range of sizes 185 1MM Figure 4. Photomicrograph of calcareous shale (silty spicular micrite). Note abundant organic matter (dark brown and black clots). Orange material is phosphatic('). Unit 14, Sliderock Mountain II section. Plane polarized light. is less substantial than those found to the southwest. nqularity of the quartz grains is characteristically high, rarely displaying a subrounded profile, while sphericity values vary greatly. few quartzose silt grains have subhedral to euhedral, bipyrimidal terminations, suggesting an authigenic origin. The possible presence of subordinate illitic clay is suggested by the absence of red stain on many cryptocrystalline elements with high birefringence and low to moderate (non-variable) relief. X-ray diffraction analysis failed to substantiate this hypothesis, due to either an insiqnificant quantity of clay, and/or masking of the illite peaks by the more intense and broader quartz peaks, which occur at similar two-theta values. Dolomite occurs locally rarely, isolated rhombs which compose up to four percent of the rock; trace amounts of cryptocrystalline dolomite cement are indicated by X-ray diffraction and fllzarin Red staining techniques. Diffractogram peak values indicate a slightly ferroan composition for these dolomitic constituents. The most significant subordinate elements, with respect to interpretations of depositional environment, are the phosphatic pellets ((2 mm diameter) and cement which occur primarily in the shales of the southwestern half of the Snowcrest Range. t the Sawtooth Mountain section many pellets, averaging 0.18 mm in diameter, compose up to 20 modal percent of the rock (fig. 44). The amorphous, golden brown pellets range from spherical and well rounded to ve'y irregular, the larger pellets tending to be more irregular in profile. Most of the pellets are golden brown in color under plane 187 polarized light, but light golden yellow varieties and all hues between also occur. ll of the pellets are isotropic under crossed nicols, although complete extinction of the entire pellet is not common. Most of the pellets have a random, honeycomb-like1 phosphatic lattice, with the very few to several intralattice spaces filled with dirty, cryptocrystalline, low-magnesium calcite as in the carbonate matrix surrounding the pellets (fig. 44). few of the pellets are isotropic throughout. The external boundaries of the pellets are sharp, but some exhibit a thin rind or envelope of dirty, cryptocrystalline calcite, distinct from the enveloping micrite surrounding the pellets. These latter pellets are characteristically 100 percent isotropic, in contrast to those lacking a calcite envelope and typically having the phosphatic honeycomb-like structure. Some of the pellets are alternately externally defined, in part or completely, by an indeterminate dark orange to brownish red material, possibly of organic origin, which surrounds the individual pellets. Where two or more pellets are in contact, a deformed margin is common, suggesting compaction while the pellets were still soft and pliable. thin, intermediary film of organic material, as just described, is common between the interpenetrating pellets. flt Hogback Mountain all of the phosphatic elements are small and irregular, lacking the well developed spherical habit common in the Sawtooth Mountain shales, and account for only two to three modal percent of the rock. Most of the phosphaticmaterial is of coarse silt size, and an appreciable amount occurs as finely disseminated, cryptocrystalline, intergranular material. Finely 1/2mm I Figure 44. Photomicrograph of phosphatic interval of calcareous shale lithofacies at Sawtooth Mountain. Phosphatic pellets (golder brown) compose approximately 2 percent of the rock. Note concavo-convex boundaries where pellets are in contact. Bioclasts predominantly sponge spicules and disarticulated ostracodes. Unit 5Z, Sawtooth Mountain section. Plane polarized light. disseminated, intergranular phosphatic material is also common in the shale at Sawtooth Mountain. X-ray diffraction analysis indicates that the phosphatic material is either fluoroapatite or possibly dahllite. In contrast, the shale at Sliderock Mountain is lacking any phosphatic pellets and appears to have only a minor cryptocrystalline phosphatic cement() constituent within the carbonate matrix. A few organic phosphatic elements, such as conodont fragments, however, are present. Ruthigenic pyrite is common as small, irregular, opaque masses disseminated throughout the shales. Many pyrite masses are intimately associated with sponge spicules, filling the canal space of the monaxons, and/or situated adjacent to the spicules. Distribution of the pyrite is otherwise non-fabric selective. Most of the masses are of medium to coarse silt size, although some display a botryoidal habit, thereby appearing as large crystal masses. As previously mentioned, laminations are common, vary in thickness, and are predominantly planar. Subtle variations in the percent of quartzose silt, percent and size of phosphatic pellets, percent and packing density of sponge spicules, crystallinity of the carbonate fraction, and the amount of organic matter and/or organic stain give rise to the laminations commonly observed in thin section. The shales become increasingly non-laminated, in general, to the northeast iithin the Snowcrest Range. Combination of the exposed and covered shale intervals, and consideration of the completely covered sections believed to be underlain by shale (based on a preponderance of uncontaminated 190 shale float) reveals that this lithofacies maintainsa relatively constant thickness of approximately 148 feet in the norterri half of the range, but thins to a zero thickness edge at the Red Rock River section (SW 1/4, NW 1/4, section 28, 1.13 5.,R. 7 W.; see plate 3). The 42 foot thickness at Sawtooth Mountain is a minimum value. The calcareous shale lithofacies crops out in a deep gully on the extreme west-southwest side of Sawtooth Mountain (NW 1/4, SE 1/4, section 8,T. 12 S.,R. 5 W.), and the upper part of the unit crops out at the base of a cliff on the north flank of the mountain (NW 1/4, SE 1/4, NE 1/4, section 9, T. 12 S.,R. 5 W.). These two exposures are separated by almost one mile and their precise stratigraphic relationship cannot be defined beyond the recognition that they are thesame lithofacies. s a result, the thickness given for this interval is that of the shale exposed in section 8, and is considered to bea minimum value. Pddition of the two exposed intervals at Sawtooth Mountain falls well below the 148 foot thickness value found to the northeast, although this does not preclude the presence ofa thicker section here as the amount of cover between the two exposures is uncertain. The apparent southwestward thinning of this lithofacies in the thesis area, therefore,may not be real. The absence of this lithofacies at the Red Rock River section is peculiar, and difficult to explain. The uppermost exposed Lombard here consists of several well exposed bryozoan and brachiopod packstone beds interbedded with silty mudstone. These are overlain by a 42 foot thick, gray soil covered interval which grades over five feet into a covered interval characterizedby 191 grayish orange to yellowish orange soil and fine sandstone float, interpreted as the basal Conover Ranch lithology. While this Lombard Limestone section is commensurate in thickness with the other Lombard sections in the Snowcrest Range,it is notably incomplete, lacking the calcareous shale and dolomitic lime mudstone lithofacies. It is also interesting to note that this is the thickest Conover Ranch section in therange (Cohn Key, personal communication, 1985), although the abrupt change in lithology from a carbonate-dominated to a clastic-dominated sequence supports this interpretation. The lower part of the Conover Ranch is very poorly exposed at this locale and an abrupt lithofacies change toa calcareous sand lithofacies, similar to that capping the Lombard (Big Snowy Formation) to the north-northwest, in the Armstead nticline area (Hildreth, 1980) is a possibility. The lack of adequate exposure, however, prohibitsa definite conclusion regarding this possibility. Plthough the calcareous shale lithofacies isa persistent and characteristic unit within the upper part of the Lombard in the Snowcrest Range it is absent to the northwest and southeast, in the Blacktail Mountains and Gravelly Range, respectively. The upper part of the Lombard at these locales is characterized by fossiliferous wackestones and packstones, and non-fossiliferous to fossiliferous mudstones. 192 Dolomitic lime mudstone lithofacies The dolomitic lime rnudstone lithofacies gradationally overlies the calcareous shale lithofacies, the transition occurring overa three to seven foot interval.This lithofacies can be subdivided into four slightly different mudstone units which vary primarily in bedding habit, percent and type of dolomite, degree of mottling, and color.These four units, from base to top, are:a medium- to thick-bedded, color mottled, dolomitic lime rnudstone (unit 1); a thick-bedded, color mottled, slightly dolomitic lime rnudstone (unit 2); a thin-bedded lime mudstone (unit 3); anda massive, dalornitic, porphyrotopic lime mudstone (unit 4), disconformably overlain by basal Conover Ranch Formation sandstone (fig. 45). Unit 1 The basal 19 feet consists of planar, medium- to thick-bedded, color-mottled, dolornitic lime mudstone.lndivtdual beds in this lowermost unit are characterized by a planar to slightly undulatory, laminated to flaggy splitting.habit, which grades laterally into locally massive beds.Color mottling is ubiquitous.Individual mottles vary from round to very irregular, and display large variations in size.Olive gray (5 V 4/1) and yellowish gray (5 V 7/2) mottles on the surface weather, respectively, from brownish gray (5 YR 4/1) and medium olive gray (5 V 5/1) mottles, visible on a cut surface.In addition, small (average 1. mm diameter), elliptical, very light gray (NB) mottlesare visible on a cut surface and tend to be located within the olivegray mottles, although they 193 -; I, 0 .:: , - Figure 4Z. Dolornitic lime mudstone lithofacies exposedin northwest-facjn cliffs on northwest flank of Sawtooth Mountain (NW 1/4, SE 1/4, NE 1/4, section , T. 12 S., R. Z W.). Lombard Limestone (Ml)-Coriover Ranch Formation(MPcr) contact illustrated by black line near top of cliffs. 194 cross-cut both the olive gray and brownish gray mottles in places. Macrofossils are not visible in outcrop and petrographic analysis reveals only a few small objects which may be very poorly preserved calcareous sponge monactines. Quartzose silt, averaging 0.014 mm (fine silt), composes less than one percent of the total constituents.The chief mineralogy of this lime mudstone, in order of abundance, includes dolomite (44 percent), raicrospar and minor psuedospar (total 30 percent), and ferroan dolomite (26 percent). The brownish gray mottles are almost entirely dolomitic (64 percent dolomite, 35 percent ferroan dolomite, and approximately one percent pseudospar).Both of the dolomitic constituents occur as limpid, euhedral to predominantly subhedral rhombs in a background of finer, mosaic dolomite.The ferroan dolomite rhombs tend to be larger than the normal dolomite rhombs.The former rhombs average approximately 11 microns in diameter, but attain sizes of 61 microns, while the latter range from 4 to 30 microns, with a mean diameter of 9 microns. In contrast, the olive gray regions consist of 60 percent dolomite and 40 percent microspar and pseudospar. No ferroan dolomite is found in these mottles.Crystal sizes of the dolomite are similar to those in the brownish gray mottles, but the mosaic microspar displays an average diameter of 10 microns.Bioturbaticiri and/or burrowing is suggested by the patchy character of the microspar and dolomite, and probably acted as the primary factor controlling their distribution.The direct influence of burrowing upon the presence and distribution of color mottling has previously been shown in Ordovician limestones of Saskatchewan arid Manitoba 195 by Kendall (1977). Well defined burrows, up to.25 mm in diameter are typically dolomite-filled, supporting the hypothesis that the dolomite distribution is controlled by bioturbation and/or burrowing. Pt least two generations of fractures cross-cut the mottles. The widest fractures are peripherally filled withcoarse, centripetal ly radiating ferroan dolomite and subordinate normal dolomite, which passes abruptly inward to similar tomosaic, low-magnesium calcite. These fractures are, in turn, cut by thin, calcite-filled fractures. Small pyrite clusters are common throughout the mudstone, although they tend to aggregate in the brownishgray mottles and are especially common near the margins of these mottles. Many of the pyrite crystals are surrounded bya golden yellow goethite stain, which is probably the result of interaction of the pyrite framboids with groundwater. Unit 2: Lower part Gradationally overlying the dolomitic lime rnudstone (unit 1) are 41 feet of variably color mottled, slightly dolomitic lime mudstone. Interbedded with the thick, planar mudstone bedsare several medium to predominantly thin, silty mudstone bedshaving a planar to undulatory, laminated to fissile splittinghabit. The thick lime mudstone beds locally display planar to slightlyundulatory, flaggy to slabby splitting habit. The lower part of this unit, displaying faint colormottling, is characterized by a pale grayishorange (10 YR 8/4) and pale brown 196 (5 YR S/2) color. Etching on a cut surface with dilute hydrochloric acid enhances the faint mottledappearance and reveals mottles having one or more yellowishgray (S V 7/2) cores, with an olive gray CS V 4/1) peripheral region, set withina light olive gray (5 V 6/1) background. In thin section the mottles are found to be composed ofa round to elliptical core of finely crystalline, mosaic dolomitewhich centrifugally grades into much coarser raicrospar and pseudospar. The peripheral zone appears to have startedas a ring of porphyroid neomorphic microspar which expanded, possibly by coalescive neomorphism, into the surrounding calcite-ankerite(?) matrix (fig. 46). Coincident with this neomorphic expansion, the microspar neomorphosed to pseudospar, some crystals attaining diametersof almost 130 microns (0.13 mm). The external margin of the pseudospar halo is very sharp, but the internal boundary isa diffuse zone of porphyroid microspar and pseudosparwhich centripetally decreases in quantity into the wholly dolomiticcore (fig. 46). The shape of the core versus the peripheralarea of the gray mottles provides an important clueto their origin, in addition to their mineralogy. These characteristicssuggest that the cores probably represent former burrows excavatedinto partially lithified micritic mud. Prior to infilling of the burrow by unconsoldated lime mud, neomorphism began in thernicrite in the burrow walls, spreading outward as long as groundwatersaturated with respect to calcium carbonate continued to circulatethrough the mud. Sometime after infilling of the burrow, butbefore lithification was 197 1/2mm I I Figure 46. Photomicrograph of mottling in dolomitic lime mudstone. Light colored mottles consist of finely crystalline, mosaic dolomite core area surrounded by coarser grained neornorphic dolomite rim. Brown background composed cf rnicrc'spar and ankeriteY). Quartz silt makes up less than two percent of the total constituents. Unit Z7,lower part, Sawtooth Mountain section. Plane polarized light. complete, the groundwater chemistry changed, dolomitizing the micritic mud in the burrow. The carbonate mineralogy surrounding the mottles is a monotonous mosaic of finely crystalline calcite and ferroan dolomite (fig. 46); X-ray diffraction analysis indicates that the ferroan dolomite is probably ankerite. Porphyroid neomorphism throughout this region has generated several isolated pseudospar crystals. A few disarticulated ostracode carapaces and sponge spicules are found in the lighter background. Quartz silt, less than 0.017 mm in diameter (fine to medium silt), makes up approximately two percent of the total constituents. As in the calcareous shale lithofacies, authigenic pyrite is common. The majority of the pyrite occurs within the calcite and ankeriteCi'), otherwise tending to collect near the outer edges of the mottles. Some of the pyrite crystals are up to 140 microns in diameter. All of the pyrite crystals have very irregular margins, and a few display fine carbonate inclusions, suggesting an authigenic origin for the pyrite. Unit 2: Upper part Upsection, the lower part of this unit grades imperceptibly into a microcrystalline, color mottled lime mudstone which megascopically differs from the lime mudstone below only in color. The dark yellowish gray and olive gray mottles below pass upward into dark yellowish orange (10 YR 6/6) mottles set against a dark yellowish brown (10 YR 4/2) background, which weather, respectively, to pale yellowish orange (10 YR 8/6) and pale yellowish brown (10 YR 6/2). Pyrite is notably absent to rare, and fine to coarse quartzose silt composes less than one percent of the rock. Calcareous sponge spicules (rnonactines), many pseudomorphically replaced by finely crystalline, mosaic dolomite, are much more common, averaging three percent of the total constituents. Ostracode debris is absent. Several irregular patches of coarse, limpid, mosaic calcite occur locally; these may represent recrystallized mollusk fragments or could be infilled burrows. Calcite predominates in this mudstone, averaging 70 percent of the total constituents, followed by dolomite at 26 percent. Ferrous dolomite within the canals of the monactines occurs in trace amounts, in contrast to the large percentage of ferrous dolomite in the lower part of this unit. Several fractures which cross-cut the upper part of this unit are exclusively filled with ferroan dolomite. dark brown iron stain defines the walls of the fractures and stains the crystal margins and cleavage traces of the carbonate fracture fill. Smaller, low-magnesium calcite-filled fractures cut these larger fractures. The mottles display only a moderate mineralogical difference from the main rock mineralogy. The mottles contain slightly more dolomite (56 percent) than calcite (40 percent), in addition to slightly more iron stain. The mottles are poorly defined because of their very diffuse margins, which are characterized by a gradual increase in calcite over dolomite, ultimately acquiring the 72 and 25 percent values, respectively, of the enclosing carbonate matrix. Despite the subtle difference in mineralogy, the calcite and dolomite in the mottles are slightly coarser than that outside of 200 the mottles. The calcite outside of the mottles is a mixture of micrite and microspar, the microspar occurring in and out of the mottles as fine, limpid, mosaic crystals. The dolomite, on the other hand, occurs chiefly as finely crystalline, limpid, subhedral to euhedral rhornbs. although pyrite is less common in the upper part of the unit, many of the crystals here appear to be intimately related to the ubiquitous iron stain which probably causes the orangish brown color of the rock. few of the pyrite crystals are surrounded by a thin halo of golden brown iron stain, which is probably goethite or limonite. Unit 3 Near the top of this lithofacies the thick beds rapidly change to thin, parallel to predominantly non-parallel, beds of dark yellowish brown (10 YR 4/2) lime mudstone, separated by very thin calcareous shale partings. The non-rhythmic, undulatory character of the top of many of the beds, averaging 1/2 inch of relief, is suggestive of ripples, although no fine-scale cross-bedding is present to substantiate this supposition. The beds, totalling six feet thick, are all massive, lack inacrofossils, and weather to a light olive gray ( V 6/1.) to light gray (N7) color. Many of the beds pinch and swell, averaging four to five inches in thicknesses. few beds display an interlocking habit akin to pieces of a jigsaw puzzle. The thin calcareous shale partings between the beds vary in thickness and continuity. Small chert stringers and nodules, typically elongate parallel to bedding, 201 are common. Dolomite is rare, occurring as very small, poorly developed rhombs which make up three percent of the rock. Ferroan dolomite is found only in trace amounts. Micrite and microspar compose 86 percent of the rock. Fine to medium quartzose silt compose a slim one percent of the rock; most is subrounded to rounded, in contrast to the predominantly subangular to angular habit of the silt in the lower 60 feet of this lithofacies. few chert grains are found intermixed with the dominant monocrystalline quartz. In contrast to the nearly non-fossiliferous character of the underlying two units, bioclasts compose almost ten percent of the this rock. Calcareous sponge spicules dominate. In addition to monaxons, a few well preserved foraminifers and disarticulated ostracode carapaces are present. Several very small, round, solid bodies of calcite also are common. These may be calcispheres, but more likely, are monactines lacking the common central canal. dditionally, several smaller (21 micron diameter), porous(?), translucent, orangish yellow objects may be well preserved pollen spores. None of the bioclasts show signs of abrasion and all are oriented parallel to bedding. Laminations are not visible in outcrop, but many subtle microtextural variations are evident in thin section. The laminations, which are visible in thin section are chiefly parallel and planar, and chiefly differ in crystallinity and abundance of allochemical constituents. Moderately densely packed spicular micrite laminae alternate with microspar-rich laminae with rare, 202 irregular patches of rnicrite and fewer sponge spicules. The monactines in the latter larnina tend to be more poorly aligned. Quartz silt and pyrite (rare> concentration does not bary between laminae. Individual lamina vary from 0.3 to 5 mm thick, the majority being approximately 2.5 mm thick. Unit 4 The uppermost unit of this lithofacies is a massive, color mottled dolomitic lime mudstone bed (one foot thick). Vertical fractures create a columnar appearance to the unit. flaggy habit is locally present. The contact with the underlying lime mudstone is sharp and slightly undulatory. The contact with the overlying basal msden sandstone bed is also sharp, but is undulatory and erosional. This contact will be discussed in more detail in a subsequent section. Moderate brown (5 YR 3/4) and medium light gray (P46) mottles characterize this unit. On a fresh surface these mottles are found to have weathered from moderate brown (5 YR 3/4) and very light olive gray (5 V 7/i) mottles, respectively. The size and shape of the mottles varies dramatically over a distance of onlya few inches. Small whitish mottles, probably representing filled burrows, tend to be concentrated near the gray and orange mottle boundaries. Microscopic analysis reveals that a few randomly oriented calcareous sponge spicules are present in the gray mottles, composing less than one percent of the total rock constituents. The orange mottles typically contain five percent medium silt-size 203 quartz, whereas the the quartz in the gray mottles seldom exceeds one percent and is chiefly fine silt-sized. Analysis of a cut surface reveals a unique fracture-bound color variation in the orangish mottles. Locally, the orange color abruptly changes to a light olive gray (S V 5/2) color across a paper thin fracture. This olive color passes back into the familiar orange color across a second, parallel fracture. No color change occurs in the gray mottles adjacent to the orange/olive mottle transition. Slight rheological variations additionally distinguish the gray and orange mottles as the thin fractures which pass throughout this unit vary in style within the separate mottles. A given calcite-filled fracture in an orange mottle will abruptly display an anastomosing habit upon passage through a gray mottle; this anastomosing habit ceases and the fracture appears to reunite into one whole fracture again, coincident with the return to an orange mottle. Mosaic dolomite and low-magnesium calcite (microspar) each compose 50 percent of the gray mottles. Both mineralogies are characterized by a relatively homogeneous grain size, averaging 6 microns, with diameters rarely reaching 23 microns. Both sets of crystals also vary from limpid to slightly cloudy. A few isolated dolomite(?) porphyrotopes, having anomalously large diameters, rarely occur within the gray mottles. The orange mottles provide a striking contrast to the monotonous gray mottles. Within the orange, very finely crystalline matrix, numerous dolomite(?) porphyrotopes aggregate (fig. 47). 204 ti.l .$ 'S r I._1mm H Figure 47. Photornicrograph of uppermost color-mottled, dolornitic lime mudstone unit (unit 59) at SawtoothMountain. Note sharp transition between orangish mottles (porphyrotopic)and gray mottles (stained red by lzarin Red solution). Note common occurrence of pyrite as nucleus of porphyrotopes. Plane polarized light. 205 Some of these porphyrotopic crystals have diameters of 220 microns (0.22 mm), and approximately 22 percent of the crystals have a pyrite core. few crystals are no longer cored by a pyrite crystal (fig. 48) ;rather, a hematite or limcr;ite ghost of the pyrite remains in its place. Rarely, the pyrite nucleus is gone and finely crystalline carbonate, identical to that of the surrounding matrix, fills the void. The crystals having a pyritic core tend to be anhedral and commonly have a few rings of orangish iron stain. These rings may be growth rings, representing brief periods of growth cessation or a prolonged decrease in the nucleation rate of the crystal, which permitted an iron stain to coat the exterior. t least two to three periods of growth are suggested by these rings. The crystals lacking the pyrite core tend to be missing the rings and are typically subhedral to rarely euhedral. ll of these crystals are characterized by a golden yellow to orangish body color and exhibit iron stained cleavage traces and peripheries. side from the few very large crystals, most are very near the average diameter of 71 microns. This suggests that the syri- and/or post-deposit ional diagenet ic microenvironment was relatively stable during the growth of these crystals. izarin Red staining indicates a slightly ferroan dolomite composition for the monotonous orange matrix which surrounds the porphyrotopes. Where the prophyrotopic crystals occur along the sharp boundary between the mottles, two different crystallization habits are noted. Most of the porphyrotopes extend unaltered into the adjacent gray mottle, but a few appear to be truncated at the trarlsitiorL (fig. 48). The reason for this is uncertain. 206 1- 1MM Figure 48. Close-up view (photomicrograph) of transition between gray and orange mottles. Gray mottles composed of 5Ipercent calcite (stained red) andø percent dolomite (white). Note pyrite cores in most dolomite(?) porphyrotopes in orangish mottles. Some porphyrotopes (arrow) display a truncated habit at the transit ion while others retain crystal habit across transition. 207 The dolomitic lime tnudstone lithofacies is exposedonly in a cliff sequence at the head of the west forkof Indian Creek, on the north flank of Sawtooth Mountain (SW 1/4, NE1/4, section 9, T.12 S.,R. W.). 1sewhere in the Snowcrest Range this lithofacies occurs as a covered, slope-forminginterval.Distinction between this lithofacies and the underlyingcalcareous shale lithofacies in a continuous coveredinterval is impossible. ny lateral variations in thickness, therefore,can only be suggested where the calcareous shale lithofaciescrops out near the identifiable base of the Conover Ranch Formation,and the intervening covered intervalcan be tentatively regarded as belonging to the dolornitic lime rnudstonelithofacies.Based on this approach, this capping Lombard lithofaciesis believed to thin to the northeast, possibly thinning to onlya few, or zero, feet at Sliderock Mountain (see plate 3).To the west-southwest, this lithofacies is missing, as is the calcareousshale lithofacies, at the Red Rock River section.The reasons for this must be thesame as those previously suggested for thecalcareous shale lithofacies. LOMBARD LIMESTONE: DEPOSI TIONAL ENVIRONMENT Introduction This chapter concentrateson the environment(s) of deposition as interpreted from field and petrographicstudies of the rocks in each lithofacies. Integration of the stratigraphic, areal, and temporal relationships of the ].ithofaciesto determine the most likely depositional setting forindividual lithofacies is reserved until the regional synthesis ina subsequent chapter. Lime mudstone lithofacies The prevalence of fine bioclasticdebris (such as sponge spicules, calcispheres, disarticulatedostracodes, and pollen spores(?)) in a micritic matrix, andthe general paucity of a shelly fauna are diagnostic ofvery low to low wave and current agitation, as is the lack of abrasion, poor sizesorting, and coctmon orientation of the bioclasts parallelor subparallel to bedding. The dark color of these rocks and thelarge amount of preserved organic matter, reflected in the strongpetroliferous odor and relatively high total organiccarbon content, additionally preclude deposition in a shallow, agitatedenvironment. The source of the small biaclastsmay be twofold. Sponges might have been indigenous to thebasin, based on the abundance of spicules in most of thesparse biomicrites which characterize this lithofacies. Sponges, however, seldom colonize muddyor silty substrates, like those whichcharacterized this lithotope, but prefer firmer substrates. Thus, the abundant spicular materialmay have 209 been carried into the thesisarea from some external source. Sponge spicules are easily transported insuspension for tens of miles with no evidence of abrasion CI.K. Rigby, personal communication, 1985), so it seems likely that thespicular debris was transported from the platform edge farther west,or from some source within the basin or along the basin margins. Monactine sponge spicules provide little useful information regarding the environment of their origin, unfortunately,since they occur in a variety of environments from hot springsto deep marine settings (deLaubenfels, 1955). The other predominant bioclasts alsoare small and readily transported in suspension, permittingan external source. Many of these particles were probably transportedinto the basin by tidal currents, and periodically by storm currents(Wilson, 1975; Sando, 1976). In contrast to the microfossils,most of the lime mud was probably produced within the basinby the disarticulation or disintegration of red or green algae (Heckel,1974). Bioturbated deposits are common throughout therocks of this lithofacies. Primary evidence of biogenic reworking of the sediment consists of peloids anda relict peloidal texture to the matrix, of burrows, of grazing trailson the bedding planes (including Helmanthosis?), anda patchy or swirled matrix fabric. Although many of these depositsappear to have hosted an abundant benthic infauna, the elongate bioclastscommonly maintain a subparallel aspect with respect to thebedding surface; this suggests that most of the sediment reworkingoccurred at the sediment-water interface or within theupper few millimeters of the 210 sediment, minimizing disruptionof the spicules and other fine bioclasts. The presence of benthic depositfeeders and grazers, and the noteworthy absence or rarity ofshelly macrofossils, suggest that the lower part of the watercolumn in the basin was dysaerobic. Field studies of modernrestricted marine basins, such as the Black Sea and the Gulf of California,have shown that marine benthos species diversity, abundance, andbody size decrease significantlyas the dissolved oxygen contentin the water column declines below 1 mI/l (Byers, t977. In general, the greatest reductionin diversity and abundance occurs in themore heavily calcified epifauna, while soft-bodied infauna, suchas polychaetes and nematodes, thrive. It seems likely, therefore, that thepresence of bioturbated deposits, and near absence ofa shelly fauna in the lime mudstone lithofacies may be explained, in part, by dysaerobicbottom conditions. Ostracodes and subordinate foraminifersand gastropods may have been indigenous to the depositional site as these animals were commonly able to withstand slightlysilty environments and dysaerobic conditions, and/or couldmaintain a position above the muddy bottom (Enos, 1983). Planar, millimeters-thick laminationsare not common in the lime rnudstones and sparselyfossiliferous wackestones of this lithofacies, but theiroccurrence in a few places suggests periodic anaerobic conditions in thedepositional environment. These intervals are t'pically onlya few inches thick and may reflect seasonal and/or episodic verticalstratification of the water column. The development of verticalstratification requires some 211 type of hydrographic or physical barrierwhich restricts or inhibits mixing of the water in the semi-enclosedsea, such as occupied the Snowcrest trough, with that in theopen ocean. Vertical mixing by seasonal turnover is generallyrestricted in hot climates because the surface water seldom cools toa temperature which will promote complete overturn of the water column. The thermocline in some equatorial seas is only 60 feet belowsea level (Ettensohn and Elam, 1985). The thermocline in the Lombardsea, therefore, may have been relatively shallow, and/orsome type of physical or hydrographic barrier may have existed atthese times near the mouth of the Snowcrest trough. Periodic introduction of terrigenousmaterial is indicated by the intermittent silty lime mudstoneintervals. The majority of this detritus is silt-sized andmay have been wind-blown from the shoreline or transported in suspensionin ebb tidal currents or longshore currents. Shaly interbeds are common in thislithofacies. Many contain a fossil assemblage similar to that in thelime mudstones, although bioclasts make up a smaller fractionof the total rock. These beds may have been deposited in lowareas in the basin floor, or may reflect periods of dysaerobicityin the lower part of the water column. Formation of a well definedpycnocline, probably associated with the thermocline,may have resulted from seasonal climatic fluctuationsor with sporadic subsidence locally within the basin which depressed thesea floor below the pycnocline. ll of the preceding featurescan be produced in either shallow or deep water environmentsin an epeiric sea. Thin layers 212 with large, disarticulated andbroken, and rarely articulated, bioclasts represent depositionfrom storm events. l3astropods, brachiopods, echinoicts, bryozoans, andpelecypods are the most common bioclasts in these storm deposits. Detrital phosphatic pellets also occur locally, signifying upwelling somewhere in the basin or nearby in the miogeosyncline. These thin deposits are relatively common, but do not display welldefined periodicity; this may indicate that deposition occurred just belownormal wave base, where the wave base associatedwith moderately energetic storms was sufficient to agitate the unconsolidatedsediment. Sedimentation associated with thesestorm events must have been relatively rapid because laminatedlime muds commonly drape and/or envelope the large bioclasts. If the sedimentation rate were slower the deposits would probably .bebioturbated. Conversely, these laminae may reflect an entire stormseason or series of storms over a given time interval which constantly reworked thesediment, destroying any biogenic structures. The laminations may initially suggest quiet water deposition, butthe excellent size sorting of the large bioclasts and textural inversionpoints to the high energy of the transporting and deposit ional currents. Vertical and horizontal stratification,which inhibits colonization of the benthos bya shelly fauna, can also be generated by the development ofa salinity gradient. In light of the restricted character of theSnowcrest trough it seems possible that the salinity in the epeiricsea was slightly above normal. Evaporite deposits are notrecognized in either the Kibbey or Lombard,, however, so the developmentof dense. hvøersaljne water 213 whichcould have migrated seawardalong the bottom of the basin seems less probable as an explanation forthe near absence of macrofossils than does the dysaerobicmodel. Fossiliferous wackestone-packstone 1ithofacies The rocks of the fossiliferouswackestorie-packstone lithofacies reflect deposition in shallow,sunlit, gently to moderately agitated water.The stalked echinoderrns,bryozoans, brachiopods, and corals which characterize this lithofaciesare all diagnostic of shallow water environments in thepresence of wave and current agitation. Several shallow water coralsoccur within the packed biomicrites of this lithofacieswhichare excellent environmental indicators. These corals are generally diagnostic of shallow (less than 50rn)1 well oxygenated, gently circulatingwater, within the photic zone. Most favor a firm substrate, clearor relatively free from the rapid accumulation of sediment (Sando,1980). Several of the solitary rugose corals, however, suchas the genus Caniriia, were able to root themselves in muddysubstrates (3.T. Dutro, Jr., personal communication, 1985).Bryozoans also favor some type of firm substrate, commonly utilizinga shell or some other large skeletal fragment, and generally requiresilt-free water (Moore et al., 1952). Several points of evidence,in addition to that provided by the primary taxa, indicate thatdeposition occurred within or above normal wave base, closerto shore.Sparry calcite is commonas both an interparticle cementand iritraparticle fill, alludingto the winnowing capacity of thecurrents in this environment.Size 214 sorting of the bioclasts is generally moderateto excellent, additionally suggesting deposition ina high energy regime. The general absence of abraded marginsan the bioclasts, however, indicates that the wave and/or currentenergy in the depositional environment was not excessive. Large parts of fenestratebryozoan fronds and partial pelmatazoan stems alsoare common to these rocks, indicating that wave and currentenergy was not strong enough to destroy these relatively fragile elements. Normal wave base in modern epicontinental lagoons andseas varies primarily as a function of the fetch of the trough. Sediments deeper than approximately 25 feetbelow sea level in Shark Bay, ustralia, are rarely subjected to reworking bywave currents. Normal wave base in the Persian Gulf, however, commonly exceeds 60 feet, and is responsible forminor reworking of sediments to depths of 100 feet. The main wind direction in both examples is parallelor subparallel to the trough axis and is from head to mouth. Similar wind patterns are inferred for the Sriowcrest trough, so wind-generatedwaves may have created a well mixed surface zone conduciveto extablishrnent of a shelly fauna to a depth of approximately 100feet. Most of the faunal elements in thesewackestones, packstones, and grainstones probably livedin or very near the site of deposition. This is particularly true of the corals. brasioru of many of the large (several inches in diameter)rugose coras collected from the packstone bedswas probably the result of iri situ water turbulence rather thantransportation over long distances ando, written communication, 1985). 215 Local encrinite accumulationsmay reflect small crinoid meadows, although deposition in lowareas on the basin floor during storm events is also a viable explanation. Rare to absent quartz in these depositssuggests that terrigenous material was not reachingthe basin during periods of fossiliferous wackestone-packstonedeposition, or that the FUbbey shoreface was far enough removed topreclude transport of sufficient quantities of clasticmaterial which could inhibit carbonate production. Conversely, moderate wave and current energy carried this material past this shallowwater environment into the deeper, quieter partsof the basin. Sponge spicules and ostracodesare present in many of the fossiliferous limestones, but generallycompose a subordinate fraction of the faunal assemblage. Sorting of the bioclasts by size is a pervasive feature in mostof the rocks in this lithofacies,as previously mentioned. Strong seaward-directed tidal currentsor waves may have winnowed these bioclasts and carriedthem to the deeper, quieter parts of thebasin, leaving behind the denser and/or larger raacrofossils. This process may explain the abundance of sponge spicules and ostracodes in the darklime mudstones to the near exclusion of macrofossils. The abundant shelly fauna issuggestive of development within the euphotic zone. The combination ofa shelly fauna, pervasive bioturbation, light colored deposits,and a low total organic content reflects a well oxygenatedenvironment. Most of the fossiliferousbeds are less than three feet thick and several appear to bediscontinuous in outcrop. Others display 216 lateral variation in bioclast abundance.The absence of evidence of in situ mud mound development suggests that most of these fossil accumulations are the result of hydrodynamic processes. The patchy distribution suggested locally by the discontinuous beds may reflect current sorting of the bioclasts into widespread centers of deposition adjacent to centers of erosion.The thin, silty and/or shaly limestone interbeds may reflect episodic or seasonal changes in the basin environment which temporarily inhibited metazoan development, or may represent rapid, lateral migration of the fossiliferous wackestone and packstone 1 ithotope.Similar discontinuous muddy packstones and coralgal grainstones are presently developing in the Persian Gulf on shoals, separated by carbonate mud-filled swales (Wilson and Jordon, 1983).Qoliths and intraclasts occur rarely, but imply that shoals were developing nearby.Such shoaling bodies may be represented by the biosparites which occur here and there in this lithofacies.Many of the biosparites contain an abraded bioclastic assemblage and are well sorted, indicating deposition in a very shallow, high energy environment. Calcareous shale and dolomitic lime mudstone lithofacies The transition from fossiliferous packstones, grainstones, and limestone lithoclast conglomerates to black, calcareous shales over an eight-foot-thick interval connotes a radical change in depositiorial environment.The e conditions (Byers, 1977). The dark color, high total organic carbon content, and common pyrite indicate reducing conditions at and below the sediment-water interface (Berner, 1970). Shales can reflect sedimentation in shallow or deep water settings. Most restricted shallow water environments, however, such as lagoons, shelves, and bays, typically lack euxinic or organic-rich carbonates (Enos, 1983). In light of the aforementioned attributes of the calcareous shale lithctfacies, these rocks probably represent deposition in a deep, vertically stratified basin. Vertical stratification of enclosed or partly enclosed basins is commonly associated with the presence of a well developed pycnocline and/or a sill, restricting horizontal exchange of bottom water with the open ocean. The latter is chiefly related to development f a thermocline and/or halocline. The thermocline in many modern equatorial seas does not exceed 60 feet below sea level. Thus, the presence of a sill at the mouth of the Sriowcrest trough, presence of a shallow thermocline, or a combination of the two may account for the anoxic bottom conditions recorded by the calcareous shales. anaerobic conditions can also occur where the oxygen minimum zone intersects the basin floor. n alternative model invoking open connection with the open ocean, therefore, may also explain the origin of these shales. The origin of the detrital phosphatic pellets in this lithofacies is unknown. Phosphatic pellets suggest nearby upwellinq to provide the nutrients necessary for rapid proliferation of planktonic and nektonic carbonate-secreting organisms which ultimately promotes 218 phosphorite precipitation at the sediment-water interface. Phosphorite deposits also have been located in estuaririe environments associated with runoff of nutrient-rich freshwater along thetlantic coastal plain (Pevear, 1966). The low humic kerogen and high sapropelic kerogen content in these shales suggests that freshwater input from rivers was minor (see petroleum potential chapter).Upwelling must have been the chief mechanism promoting nearby phosphorite precipitation.The detrital character of the pellets indicates an origin external to the study area, although the absence of coarse, hydrodynamically equivalent bioclastic material suggests that the source was close. In addition to the inhibition of metazoans by anoxic bottom conditions, the moderate quartz silt and sand content may have limited establishment of filter feeders, although mollusks, ostracodes, and annelids can all exist in silty water (Heckel, 1972); these are not found in the shales, however. naerobicity in the lower part of the water column, therefore, is interpreted as the main factor inhibiting the presence of an infaunal or epifaurial taxa. The gradational transition to the dolomitic lime rnudstcine reflects a slow change in the depositional environment. The near absence of bioclasts in the dolomitic lime rnudstones signifies continuation of a stressful benthic environment which inhibited establishment of a shelly epifauna.The color mottling which characterizes these rocks, however, reflects a subtle change in the environment which permitted the reintroduction of a benthic infauana.It is apparent that the stratified water column which 219 previously existed broke down or vertical (thermal) mixing slightly increased, causing replacement of the anaerobic bottom conditions by dysaerobic conditions. The slight increase in dissolved oxygen content in the deposit ional environment is also suggested by the marked color change of the rocks from black and dark gray to light brown. Slow sedimentation rates may also explain the paucity of bioclastic debris. Long-term exposure at the sediment-water interface allows time for chemical dissolution and/or mechanical breakdown by benthic scavengers. Many of the mottles appear to display two periods of burrowing. Kendall (1977) has observed similar relationships in color mottled Ordovician dolomites in Canada. Early lithification of the sediment restricted the second generation of burrowing to the unlithified first generation burrows. Such a process may have occurred in the Lombard dolomitic lime mudstones. The increased oxygen content in the lower part of the water column may be the result of major changes in the basin configuration which promoted a deepening of normal wave base, shallowing of the basin as a whole, and/or decreased restriction across a carbonate sill at the mouth of the trough. Destabilization of the pycnocline may be associated with any of these changes. The origin of the dolomite is unknown. Evidence of continuous or intermittent subaerial exposure is absent, so seepage ref lux on a tidal flat seems unlikely. Development of a meteoric mixing system, however, similar to that proposed to explain the doloraitizat ion of the lower to middle Paleozoic carbonate rocks of 220 the Cordilleran miogeocline of Nevada (Dunham and Olson, 197B) may explain the extensive dolomitization in the uppermost Lombard carbonates. That the dolomite distribution coincides with the burrowing indicates that the burrowing preceded the dolomitization event. The large dolomite porphyrotopes in the uppermost part of this lithofacies (unit 4) suggest a lengthy period of stable physico-chemical conditions conducive to extended growth of the crystal, although the scattered zoned(?) porphyrotopes suggest several periods of instability. The paucity of well zoned porphyrotopes suggests that the times of instability were relatively brief and that moderately stable environmental conditions were the rule. Reducing conditions in the sediment are indicated by the abundant pyrite at many levels in the lithofacies. The pyrite does not directly indicate negative Eh values in the lower part of the water column, but does suggest that conditions at the sediment-water interface, or just below may have been slightly reducing. Conversely, some of the pyrite may have originated from the same formation fluids which dolomitized the lime mudstones. Structures and petrographic features diagnostic of deposition or a tidal flat are absent. It seems likely, therefore, that deposition occurred in a moderately deep basin, below wave base and possibly at the lower level of the photic zone. 221 flGE OF THE LOMBARD LIMESTONE Early workers correlated the Otter and Heath Formations in the Big Snowy trough to the Big Snowy Formation insouthwestern Montana, assigning a Chesterian age to these rocks (Maughanand Roberts, 1967; Roberts, 1979). Recent studies have confirmed that the Lombard Limestone is correlative to the Otter andHeath, but is older than these units in the west and is, therefore,diachronous to the northeast. Conodont, coral, foraminifera, and brachiopod collections from the Tendoy Mountains, near the Montana-Idaho border,provide a late Meramecian through late Chesterianage for the Lombard (fig. 49; Sando et al., 1985). Conodont collections in the Bridger Range, however, indicate that the Lombard is entirely of earlyto late Chesterian age (Guthrie, L984). The lower part of the Lombard in southwesternmost Montana is commonly poorlyexposed, precluding the collection of biostratigraphically usefulfossils (B.R. Wardlaw, personal communication, 1985). Thus, the more resistant upper part of the Lombard is typically theonly source of fossils diagnostic for age in the Lombard. Such is the case in the study area. Eighty-three collections of corals, brachiopods,bryozoans, and pelecypods from the Lombard were made in the Snowcrestand Gravelly Ranges, and at Sheep Creek Canyon. These collections yielded 21 coral and brachiopod species ofwhich most are specifically diagnostic of Chesterianage (Foraminifera Zone 161 to 18; U. J. Sando and J.1. Dutro, Jr., written communication, 1985); SOURCESI: FOR AGES AND RELATIONSHIPS OF UNITS communication,StammSkipp et(1984); al. P.1985; E. lsaacson,B. personal (1979); Dutro et al. R. Wardlaw, (1984); II; SandoPecorapersonal et (1985) al.communication, 1985; Wardlaw and (1975); Brewster (1984); YiXiFOSSIL ZONATION, WesternNametBamber, Foraminiferal United 1969) States Zones Negafaunal (Mamet Zonesand personalSandoC.Guthrie F. etKey, (1984); al.communication; personal Hadley communication, et Wardlaw al. 1985; (1985); B. R. Wardlaw, (1980); nd Zi Sando1979)(Sando, Coral Mamet,Zones (Sandoand Dutro, and Bamber,1969) III: Hadley (1950); Sloss and Moritz (1950); DavisHarrisPecora (1983). (1972);(1985); SandoThis report.et al. (1975); Montana,relationshipsFigure 49. and central of Late Montana. Mississippian units in east-central Idaho, southwestern Time-stratigraphic chart showing (following page) temporal Compiled and modified by the author from sources listed above N) -- EI1TRAL DA$IO $OIJflS1BI$ MOSUN WITIt*L ItITAM $.u$hiia list I.aisiisd Tis.y ,g4,, Lvii aid Miss. 3 1 Miss. is... .c1 I II . UI D.vils pocketvm. Snaky Cony.. Formation Quadrant Fora.floi - ______iiu.blrd Moisstali FormsUom Ais.ksieflChLs. I Arco Hills Formation .,m.tIoa fyi.r Fm. Il siih c - Surreti Canyon a, Formation j Heath Fm. Railroad 5 pm. 5 - CaonFa. %ØitO* south Cr..k i 'er.aiIo I _.!} scott Peak F.rm.tl.a 0 0 / Middle Canyon Formation c ChaIeS Mission Mission Canyon LIm.ston. __! Figure 49 (continusd)s Data sources and fossil zonation legend shownon previous page. (A) 224 these collections are listedon Table 2. Two additional corals, diagnostic of Osagean to early Meramecianage, were also identified from a thrust slice(?) of Lodgepoleor Mission Canyon Limestone within one Lombard section. All of the corals collected from the Lombard in theSnowcrest Range occurred in rocks of the fossiliferouswackestone-packstone lithofacies in the upper half of the formation(tongues IVS-VIS). Two of these corals, Sihonophvlliasp. and 9. excentrica Meek, are diagnostic for Coral Zone V (early and late Chesterian;Sando and Bamber, 1979). Amplexizahrentis sp. and Michelinia cf. meekana Girty are long-ranging species indicative only of Mississippian time. Several specimens of the tabulate coral DuncanoDorasp. occur in a fossiliferous wackestone bed 37 feet belowthe top of the Lombard at Sheep Creek Canyon. Three thick, limestone beds crop out approximately 203 feet lower, whichcontain an abundant assemblage of solitary and colonialrugose corals. "seudodorlodotia"? sp. and Multithecapora morphogroup Aare present in these beds and are diagnostic of CoralZone VB and XV to VA, respectively (W. J. Sando, writtencommunication, 1985); these corals correspond, respectively,to late Chesterian and late Meramecian through early Chesterian time. Fourteen different brachiopod specieswere identified from the Lombard in the Snowcrest Range (table2). All of these brachiopods are Chesterian inage, approximately equivalent to Foraminifera Zones iGi through 17 (J.1. Dutro, Jr.., written communication, 1985). The lowest identified brachiopod collected in 225 LIST OF FOSSILS RECOVERED IN LOMBARD LIMESTONE: SNOWCREST,BLACKTAIL, AND GRAVELLY RANGES Section location Coral taxa Unit(s) Red Rock River Siohonophyllisp. 82, 84, 111 Clover Divide Vesjculophvllum sp. Mission Dihvhvl1um sp. Canyon Fm. Sawtooth Mountain Amplexizaphrentjs sp. SiDhonoohvllia sp. 43, 50 Michelinia cf. M. ineekana Girty 50 Hogback Mountain Michelinia cf. nieekana Girty 7 Siohonoohyllia sp. 30 Sliderock Mountain Dissepimented horn coral, indet. 18 CI) Amplexizaphrentis sp. 11 (II) SiDhonoDhyllia ep. 11 (II) Vesiculophylluin sp. 11 (II) Ampl.xoid coral, indet. 11 CII) Clover Meadow AmDlexizaphrentis large sp. I Siphonophyllia sp. 2, 4 Sheep Creek Canyon Duncan000ra sp. 37' below top Amplexizaphrentis ep. 47' below top Siphonophyllia ep. 203' below Siohonoohyllia sp. top (semicolonial) '1Pseudodorlodotia" sp Il Multithecoora morphogroupA Brachi000d and oelecvod taxa Red Rock River Ovatia cf. mural is Gordon 69 Limipectin cf. L. otterensis Easton 69 Neospirifer praenuntius Easton 82 Chonetes sp.7 92 Table 2. List of fossils collected in studyarea. 226 LIST OF FOSSILS RECOVERED IN LOMBARD LIMESTONE: (CONTINUED) Section Brachi000d and pelecyood taxa Unit(s) Clover Divide Rntthuatonia aff. Dernodosa East on 55 Anthracospiri fer urvilateralis Easton 55, float Comoosita ep. 57 Comoosita cf. Q2.. subouadrata Hall float Sawtooth Mountain Spirifer cf. S. brazerianus 22 Anthracosoiri fer curvilateraljEaston 31 ComDosit.a sp. 39, 45 Ant thuatonia aff. 9. oernodoea East on 50 Inflatia aff. richardsi Sirty 50 Anthracospiri fer w'vialteralis Easton 50 Sliderock Mountain Inflatia cf. I. obsoletus Easton 18(I) large honetes sp. 18(I) Orthotetaceans, indet. 38(I) Antipuatpnia sp. 10/11(II) Inflatia cf. k. obsoletus Easton 10/il(II) inflatia sp. 10/11CII) Flexaria sp. 10/11(11) DiaDhraumus cf. centriensis Worthen 10/11(II) Anthracospiri fer curvilateralis Easton 10/11(II) Composita cf. sulcata Weller 10/it(II) Snowcrest Mountain Inflatfa sp. 51 Inflatia sp. 52 Sirifer sp. (possibly razerianus t3irty) 52 Ant ipuatonia' sp. 52 Table 2 (continued). 227 the Lombard of the Snowcrest Range isa specimen of Inflatia cf. j.. obsoletus Easton, which occurred 210 feet above thebase of the Sliderock Mountain I section. Several specimens of Anthracosirifer cf. A. curvilateralis Eastonoccur in the upper two-thirds of the Lombard throughout therange. This brachiopod is generally diagnostic of Foraminifera Zone17 (early late to middle late Chesterian; J. T. Dutro, Jr.,written communication, 1985). The majority of the brachiopods collected occurredin the upper half of the Lombard. The age of the lower half of the Lombard in thestudy area is uncertain, but can be ascertained by correlatingwith ages determined for the same interval in adjacentareas. Recent conodont collections in the Basin Creekarea (fig. 2), at the southwesternmost extension of the Snowcrest Rangehave documinted a late Meramecian to earliestCliesterian age (Foraminifera Zone 14-161) for the basalLombard (B.R. Wardlaw, personal communication, 1985). Northeast of the study area, at Baldy Mountain, the lowest part of theLombard is covered, but the oldest exposed fossiliferous units yieldan early Chesterian age (Hadley et al, 1984; B.R. Wardlaw, personal communication, 1985). Thus, the lower half of the Lombardmay be as old as late Meramecian (Foraminifera Zone 14 and 15), butis no younger than earliest Chesterian (Foraminifera Zone 16i,lower part). The base of the Lombard, therefore, isprobably also slightly diachronous to the northeast in the studyarea (fig. 49). The upper half of the Lombard in thestudy area is entirely Chesterian based on of the widespreadoccurrence of corals 228 diagnostic of this age in all tongues above IVS (see plate 3). Chesterian corals also occur in the lower part of the Lombard at the type section locality in the Horseshoe Hillsarea, near Toton, Montana (B.R. Wardlaw, personal communication, 1985). Thus, the upper half of the Lombard in the Snowcrest Range is correlative with most, if not all, of the Lombard at the northeasternend of the Late Mississippian Snowcrest trough. This confirms the diachronous character of the Lombard Limestone in southwestern Montana. The age of the uppermost Lombard in the studyarea is unknown. Several brachiopods, including Orthotetes kaskaskiensis bransonorum Gordon, Composita cf. C. poposiensis Gordon, Anthracospirifer welleri lincolnensis Gordon, nthracospirifer aff. occiduus Sadlick, and Orbiculoidea cf.Qwyominpensis Branson and Greger, were collected from a thick limestone interval inthe overlying Conover Ranch in the Snowcrest Range (C. F. Key, written communication, 1985). These brachiopod taxa are diagnostic of late to latest Chesterian time (ForaminiferaZone 18, upper part, to 19). The uppermost, undated calcareous shales anddolomitie lime rnudstones, therefore, are probablyno younger than late to latest Chesterian (Foraminifera Zone 18 to19, lowest part) in age (fig. 49). This age corresponds well with that determined fr the uppermost Lombard and Heath elsewhere in southwesternand central Montana. Comparison with Late Mississippian units to the east,south, and west reveal that the Lombard iscorrelative, respectively, to the Otter and Heath Formations in centralMontana (Big Snowy 229 trough); Horseshoe Shale and Moffatt Trail Members of the msden Formation in west and west-central Wyoming (Wyoming basin); and Scott Peak (upper half), South Creek, Railroad Canyon, and Surrett Canyon (lower 400 feet) Formations in east-central Idaho (outer cratonic platform) (Easton, 1962; Huh, 1967; Maughan and Roberts, 1967; Mamet et al., 1971; Gordon, 1975; Sando, 1975; Sando et al., 1975; Sando et al., 198!; Wardlaw and Pecora, 1985; S. 1. Dutro, Jr., personal communication, 1985). These relationships are diagramatically illustrated on Figure 49. 230 RELATIONSHIP OF THE LOMBRRD LIMESTONE TO THE OVERLYING CONOVER RANCH FORMATION The Lombard-Conover Ranch contact is poorly exposed throughout most of southwestern and central Montana. Subsurface and scattered surface exposures indicatean unconformable relationship between the correlative Heath and TylerFormations east of the Lombard arch, in the Big Snowy trough(fig. 9; Harris, 1972; Sando et al., 1975). West of the Lombard arch, in the Bridger Range, the Lombard-Conover Ranch contactis marked by a duracrust (caliche), which signifiesan extended period of subaerial exposure prior to Conover Ranch deposition (Guthrie, 1984). The disconformity recognized in the Bridger Rangeis extended southwest to Baldy Mountain, but is not recognizedsouthwest of the this area by Hadley and others (1984). In the Tendoy Mountains, conodont and coral data indicate thatthe Lombard is conformably overlain by the Conover Ranch (Sandoet al., 1985). Hildreth (1980, 1981) has also recognizeda gradational contact in the Armstead anticline area, characterizedby increasingly sandy, packed biomicrites of Conover Ranchaffinity. Owing to the non-resistant character of the calcareousshales and dolomitic lime mudstones of theuppermost Lombard and siltstones and mudstones of the basal ConoverRanch, this contact is very poorly exposed at most localitiesin the thesis area. An excellent cliff exposure of the contact,however, occurs at Sawtooth Mountain (fig. 2). The transition here occurs as a sharp lithologic break from lightgray, color mottled, dolomitic lime mudstone to massive, calcite-cemented quartzarenite (fig. 50). The 231 Figure 5. Lombard Limestone-Conover Ranch Formation transition exposed in cliff exposure at Sawtooth Mountain (NW 1/4, SE 1/4, NE 1/4, section 9, T. 12 S., R. 5 W.; also see figure 4). Black line demarcates disconformable contact. Black numbers of metal rule occur at one inch increments. 232 contact is undulatory with at least two inches of relief. Flaggy parting units at the top of the lime rnudstoneare commonly truncated against the troughs of the undulatory surface, suggesting a period of erosion before or during deposition of the sands (fig. 51). Angular to subrounded lime mudstone rip-up clasts also occur at the base of the sandstone, especially in the troughs. No evidence of caliche developmentwas found along the contact. An abrupt change in deposit ional environmentacross this Lombard-Conover Ranch transition is also evident at Sheep Creek Canyon, although direct superposition of these twounits does not occur. A two foot thick, buff, clayey interval separates the limestone lithoclast conglomerates of the basal ConoverRanch from the underlying fossiliferous wackestones and mudstonesof the Lombard. This thin, covered interval probably represents post-Lombard, pre-Conover Ranch soil development CE. K.Maughan,. personal communication, 1985). The calcareous shales and dolomitic lime mudstones which characterize thethe uppermost Lombard in the Snowcrest Range are not present here. The shales and dolomitic lime mudstonesare also absent at the Lombard-Conover Ranch transitionat Clover Meadow, in the north-central Gravelly Range (fig. 2). The uppermost Lombard consists of deeply weathered,sparse biomicrites overlain by sucrosic dolomites of the basal Conover Ranch. The contact between these two units is obscured by a thin soiland vegetation interval (fig. 39). The amount of Lombard Limestone missing ateach of these sections is uncertain. The complete absence of calcareous shales 233 Figure 51. Close-up view ofLombard Lirnestone-Conover Formation contact. Ranch Note undulatorycharacter of contact and truncation of flaggyparting units in mudstones. uppermost dolornitic lime pproximately two inchesof reliefoccurs along the contact in the lefthalf of the photograph. 234 and dolomitic lime mudstones at Sheep Creek Canyonand Clover Meadow suggests extensive uplift and erosion precededConover Ranch deposition. Major lateral facies changes in the uppermost Lombard may also account for the observed variationin litholoqy immediately below the contact. The erosional, undulatory character of the the contact at Sawtooth Mountain andpresence of a paleosol (?) on the top of the Lombard atSheep Creek Canyon implies a disconformable relationship between the twounits. Tha absenceof biostratigraphically useful fossilsdirectly above and below the tran*ition precludesany precise statement regard ing the duration of the hiatusrepresntedby the contact. The lack of laterallyóntinuous outorops along which the transition can be traced also inhibits recognition of angularrelationship or gradational changes. Thus, the disconformity observed in outcrop ..may be better classified as a diastern. The inferred disconformable character of the contact at both SawtoothMountain and Sheep Creek Canyon indicates that the regionalLombard-Conover Ranch contact should be extended into the SnowcrestRange-Blacktail Mountains area. 235 LOMBRRD LIMESTONE DEPOSITIONAL MODEL Early late to late Meramecian Following initial subsidence of theSnowcrest trough and nearshore deposition of the KibbeyFormation in middle Meramecian time, the southwestern end of thetrough subsided rapidly. This abrupt change in the deposit ionalenvironment is reflected in the initiation of carbonate depositionin the study area. Two rna.jor mechanisms may account for this pronouncedchange inbasin sedimentation. First, accelerated basin subsidenceand the resulting marine flooding of the basin in early lateMeramecian time caused the siliciclastic-dominated Kibbey shoreface tomigrate northeastward within the trough. The absence of an interfingering relationship between the basal Lombard andupper Kibbey in the study area and elsewhere in southwestern Montana,and the abrupt appearance of carbonate deposits on Kibbeysandstones and siltstönes indicatea rapid change in relativesea level with a lateral shift of the Kibbey depositional environment. A rapid eustatic rise insea level is not envisioned as the cause of thisflooding event because the record of rising sea level documentedin the Amsden Group of the time-equivalent Wyoming basin indicatesa constant and progressive rise in sea level from lateMeramecian through Pennsylvanian time (Sando et al., 1.9Th). A carbonate bank complex (ScottPeak Formation) to the west on the outer cratonic platform continuedto upbuild throughout this time (Stamm, 1984; P. E.Isaacson, personal communication, 1985), 236 acting as a submerged sill at the mouth of the subsiding Snowcrest trough. This complex also was present during Kibbey deposition, confining terrestrial sedimentation to the trough (Sando, 1976; plate 4-A). That the carbonate bank was not drowned during late Meramecian time implies that a rapid eustatic sea level rise probably did not occur, or that upbuilding of the bank keptpace with the rising sea level. If a rise in relative sea level occurred it was brief and did not radically alter continued development of the bank complex (P. E. Isaacson, personal communication, 198). Second, clastic input into the deposit ional basin was substantially diminished, permitting the introduction and proliferation of carbonate-secreting organisms and carbonate detritus into the basin. This cessation of terrigenous influx may reflect a reduction of the sand and silt supply atsource areas to the northeast and possibly the north. Alternatively, mild elevation of the Lombard arch at this timemay have restricted connect ion of the basin with the clastic sourcearea to the northeast. More significantly, the northeastward migration of the Kibbey shoreface resulted in entrapment of most terrigenous detritus by Kibbey tidal flat, estuarine, and foreshoreareas near the head of the trough. A region of mixing of the Lombard carbonates and Kibbey foreshore clastics may have existed somewhere northeast of the studyarea. It is apparent that subsidence in the southwestern end of the Snowcrest trough occurred simultaneously with tectonic elevation, stability, or slower subsidence of the outer platform-bank complex (plate 4-A). In concert with increased subsidence in the Snowcrest trough, uplift of the east-west-trending southern Montana arch 237 began separating the Snowcrest trough and Wyoming basin (Sando, 1976; fig. 7). Thus, by late Meramecian time the Snowcrest trough had become a well defined basin. Because the amount of positive topographic relief attained by the bank relative to the Snowcrest trough is uncertain, the degree of restriction over the bank is unknown. Some restriction is evident, however, as the lower part of the Lombard package is dominated by dark, spicular lime mudstones displaying evidence of deposition in quiet, dysaerobic water (lime mudstone lithofacies). Analysis of the intertonguing relationship between the lime mudstone and fossiliferous wackestone-packstone lithofacies with respect to the position of the mouth and head of the Snowcrest trough suggests that the former lithofacies represents deep water deposition, below normal wave base, whereas the latter reflects shallow water deposition above normal wave base (see Plates 3 and 4-B). Three lithofacies belts are recognized which shifted laterally in the Snowcrest trough throughout Lombard deposition. These facies belts correspond well with those predicted by Shaw (1964) and Irwin (1965). They suggested that three facies belts should develop in an epeiric sea in which depositional strike approximately parallels the basin margins. The seaward belt reflects deposition below normal wave base; the intermediate belt documents deposition in shallow, agitated water where normalwave base and the basin floor intersect; and a landward belt is also developed in shallow water, but under less agitated conditions because most of thewave energy is damped across the intermediate facies belt. The southwestern part of the basin was deep and vertically 238 stratified, as represented by the thick accumulation of dark, organic-rich, spicular mudstones found in all Lombard sections exposed southwest of the Sliderock Mountain area (Plate 3).These rocks were deposited below wave base under dysaerobic conditions which precluded habitation by a shelly epifauna, but allowed soft-bodied infauna to thrive. The silling effect of the bank complex was apparently effective enough to reduce or inhibit mixing of the Lombard sea with the open ocean, promoting development of a vertically stratified Lombard sea. Periodic increase in the degree of restriction and/or elevation of the pycnocline (Byers, 1977) caused anoxic bottom .water conditions, manifest in the laminated lime mudstone intervals. Episodic storm events transported bioclasticmaterial and phosphatic pellets from the shallow bank environment and/or métazoan-rich, shallow water facies belt into the deeper parts of the basin, resulting in deposition of thin, macrofossil-rich beds. The detrital phosphatic pellets suggest that upwelling processes were operating along the bank, ultimately promoting phosphorite formation. Shallow water deposition occurred in the northeastern part of the basin, where intersection of the basin floor and normalwave base resulted in slightly to moderately turbulent, well oxygenated water (plate 3). diverse shelly fauna, dominated by stalked echinoderms, bryozoans, and brachiopods was established in this part of the basin. s these faunal constituents died and were disarticulated, moderately energetic waves and currents redistributed the bioclasts into broad, sheet-like deposits. Proliferation of the carbonate-secreting organisms and the production of additional 239 carbonate detritus caused upbuilding toward sea level and deposition of more mature limestones, such as biosparites and biopelsparites. Upon nearing sea level deposition of the fossiliferous limestones spread laterally, progradingsouthwestward over the deeper water lime mudstone deposits (Plate 3). Farther northeast and along the trough margins, the siliciclastic Kibbey tidal flat and shoreface deposits continued to develop and migrate up the trough as sea level rose and/or basin subsidence continued (plate 4-B). Wave energy in this environment was probably very low as a result of damping of the waves and tidal currents across the shallow water, fossiliferous wackestone-packstone belt. The threefold facies pattern which existed in the basin during the early period of Lombard deposition indicates that subsidence was greatest to the southwest and progressively less to the northeast. Thus, a gentle ramp was established, which was truncated somewhere west of the study area against the eastern side of the Scott Peak bank complex (plate 4-B). Following initial differential subsidence which produceda down-to-the-southwest basin profile, subsidence rates appear to have remained uniform throughout the trough. thick lime mudstone lithofacies sequence was consequently deposited in the southwestern half of the study area, while thin fossiliferous wackestone-packstone tongues developed and episodically prograded westward in the northeastern part (Plate 3). Plthough subsidence was probably uniform throughout the trough, one major overprinting relationshipcan be recognized and a 240 second inferred in the Lombard stratigraphic record. First, the thin fossiliferous wackestone-packstone tongues, separated by northeastward-pinching lime mudstone tongues, indicate that in the northeastern part of the trough (a) basin subsidence was episodic, (b) rising sea level periodically outpaced carbonate buildup and progradat ion, or (c) a combination of the two occurred. Thus, the shallow-water tongues reflect cyclic re-establishment and lateral progradation of the shelly fauna deposits, followed by drowning and ret rogradat ion. Most of the lateral and vertical transitions from the deep to shallow water lithofacies are gradational, connoting gradual, though episodic, subsidence. However, sharp basal contacts and lithological transitions between some deep water and superjacent shallow water deposits, such as occur at the base of tongue IllS at Snowcrest Mountain, imply abrupt cessation of subsidence and possible slight uplift of isolated areas at the northeastern part of the trough. Second, basin subsidence and/or rising sea level may have migrated northeastward, enlarging the depositional basin. This is suggested on Plate 3 by the progressive northeastward advance of the lime rnudstone tongues during deposition of the lower part of the Lombard. In the absence of data on the Lombard between the Greenhorn Range and Horseshoe Hillsarea (fig.1; plate 3) this ideal northeastward migration of the episodic deep water facies cannot be firmly established. The lower half of the Lombard in the Tendoy Range area, however, is late Meramecian inaqe (Sando et al., 198), while the Lombard in the Bridger Range is entirely Chesterian (Guthrie, 1984). Progressive northeastward expansion of 241 the deposit ional basin is also suggested by isopach data of complete Lombard sections which are significantly thinner toward the head of the trough (figs. Z2 and 3). diachronous relationship within and between the Kibbey and Lombard is thus established (fig. 49). Episodic migration of the deep water facies to the northeast, therefore, seems probable in light of the hypothesis thata gradual, progressive eustatjc rise in sea level occurred during Kibbey and Lombard time. It is interesting to note that the shallow-water facies tongues appear to have migrated progressively southwestward upsection in the lower part of the Lombard, establishinga mirror-image type of symmetry relative to the deep water facies tongues (plate 3). Progressive elevation of sea levelmay have accentuated tectonic fluctuations in the trough creating a pendulum-like relationship between the tongues. This apparent mirror-image relationship may not exist, however, as the lateral extent of the individual tongues is poorly defined on outcrop. The lower part of the Lombard, dominated by the lime mudetone lithofacies, is inferred to be late Meramecian inage. This age is suggested by the intimatelithostratigraphic relationship between the carbonate bank complex (Scott Peak Formation)and the deep, quiet water lime rnudstones depositedbehind the restricting bank (plate 4-B). Upbuilding of the carbonate occurred from middle Meramecjan (Foraminifera Zone 13)to latest Meramecian-eari jest Chesterjan time (Foraminifera Zone15-16i; Stamm, 1984). late Merasnecian age for the lower part of the Lombard, therefore, is indicated by both biostratigraphicand MONTANA ...,,I Is I. /'$\ Its SSSSSeT / ,_ ',_!-z--" I a. I, W / ISOPACH MAP OF ThE LOMBARD UMESTONEIN SOUTHWESTERN MONTANA It r ails " I utsIstuas Figure 52. Isopach map of the Lombard Limestone in southwesternMontana. Contour interval Is 100 feet. Figure by the author. N) N) :.' I V I' f-i Jj ---P1 -I (' -. 'I .',4 I - t ., J _ _r .-lI ) - V J; ) - T , : r,-I I '-I ' & , -. - (_ I_J__.-c - -.'l . ,,-t4_. S. -r - . . u - - - , 244 1 ithostrat igraphic evidence. Early to middle late Chesterian In earliest Chesterian time (Foraminifera Zone 16i)a pronounced change in the deposit ional environment took placeon the edge of the outer platform. The Scott Peak bank complex, which persisted throughout middle and late Merameciantime, ceased developing in response to an abrupt deepening event (Skippet al., 1979; Stamm, 1984). Carbonate bank deposition as far east as the Beaverhead Mountains area,during the Meramecian,was replaced by deposition of barren, limy siltstones and claystones of theRailroad Canyon Formation, and silty, argillaceous limemudstones of the South Creek Formation (plate 4-C; Wardlaw and Pecora,1985; Skipp et al;, 1979). The laminations and fissile splitting habiton outcrop suggest deposition in deep water, below normalwave base, and probably below or in the lower reaches of thephotic zone. Increased subsidence, or a rise insea level which exceeded bank sedimentation, or a combination of theseprocesses may explain this drowning event. Deepening of the sea across the bank probably initiated improved circulation in the Snowcrest trough,enhancing mixing of the basin water with theopen ocean. The vertically stratified, dysaerobic basin water was consequently replacedwith aerobic water, permitting a rapid proliferation ofthe shelly fauna. The upper part of the Lombard consists predominantly of fossiliferous wackestones and packstones, and subordinateqraInstones, diagnostic of shallow-water sedimentation (tonguesIVS-VIS). Shoaling in the 246 initiated (plate 4-C and 4-D). In light of the thick fossiliferous wackestone-packstone package which characterizes theupper part of the Lombard in the studyarea, however, basin subsidence and/ar elevation of sea level must have continued(see plate 3). Proliferation of the carbonate secreting organismsin the shallow, agitated, silt-free basinmay have induced a high sedimentation rate which maintained equilibrium with,or exceeded, basin subsidence, generating the thick shallow water limestonesequence. The thinner South Creek and Railroad CanyonFormations, which reflect the deepening event on the outer cratonicplatform, may have resulted from: (1) tectonic subsidenceexceeding upbuildirig, and/or (2) inhibition of the carbonate-secretingepifauna by increased water depth, dysaerobic bottom waterconditions, and/or silt-laden water. Deeper water sedimentationon the outer platform (South Creek and Railroad Canyon Formations)thus passed northeastward into a shallow marine deposit ionalenvironment (upper part of the Lombard) during early Chesterian time(plate 4-D). This deep-to-the-west, shallow-to-the-eastrelationship appears to have prevailed throughout most ofupper Lombard and Railroad Canyon deposition; the lower 439feet of the 676 foot thick Railroad Canyon section consists oflimy claystones, siltstones, mudstones, and shales (Wardlaw and Pecora,198Z). Rare grainstones, wackestones (sparse biomicrites),and mud chip-bioclast limestone conglomerates in themiddle third of the Railroad Canyon (Wardlaw and Pecora, 1985), however,suggest that sedimentation near the mouth of the Snowcrest trough occurredclose enough to d by slight deepenings of the wave 247 base, drops in sea level,or depositional upbuilding to this zone of agitation. Conversely, some of the rare depositsmay reflect catastrophic sedimentation associated withMajor storm events and/or turbidity currents generatedin the east, south, or north. t the extreme southwestern end of thethesis area the thick, fossiliferous upper Lombardsequence splits into three thick tongues (IVS, VS, VIS). These are separated by two thick deep-waterlime mudstone tongues (VD, VID), whichsuccessively display a southwestward aspect higher in the section(plate 3). This part of the trough, therefore, actedas a transition zone between shallow and deep water deposition, possiblyin response to differential subsidence across this zoneor a slight increase in bottom slope to the west. The two major lime mudstone tonguesgenerally are identical to the lime mudstone tongues in thelower part of the Lombard. The absence of a carbonate bankto the west at this time (early Chesterian to middle late Chesterian)precludes employment of a vertically stratified, sillëd basinmodel to explain the lack of a shelly fauna and abundant infauna. Perhaps these quiet water deposits reflect sedimentationon a gently seaward-dipping, distally steepened ramp, well below the normalwave base where the top of the oxygen minimum zone impingedupon the platform. Silt is a moderately common constituent inthe carbonates of the Railroad Canyon Formation to the west, butseldom exceeds six percent in the lime niudstone beds in thestudy area. Thus, silting of the water cannot be calledupon to explain the decreased carbonate production. P second possibility is that thedrowned bank complex maintained slight positive reliefadjacent to a slightly negative topographic depression in the basinfloor at the southwesternmost end of the trough. Such a relationship may have produced local anaerobic bottom conditions in the small,gently silled basin. similar model has been employedto explain the occurrence and distribution of the laminatedlimestone facies of the middle Silurian Roberts Mountain Formation (Mattiand McKee, 1977). Vertical "bobbing" of this local instabilitymight also explain the twice-repeated transition from deepdysaerobic to shallow aerobic sedimentation. The uppermost shallow water tonguethins slightly to the southwest, and progrades out ofthe thesis area. Several specimens of SiDhonoohvllia sp.are present in this tongue at the southwesternmost section in the studyarea, indicating early to late Chesterian deposition (ForaminiferaZone 16i to middle 18). The presence of similar corals, Siphonophylliasp. and excentrica Meek, at the base of the fossiliferousupper Lombard section, approximately 360 feet lower in thesection, suggests that this tongue should be assigneda late Chesterian age. The uppermost part of theRailroad Canyon Formation is a 5-foot thick cross-laminatedsiltstone and limestone interval which is temporally correlative tothe Conover Ranch Formation (Ward law and Pecora, 198). Directly underlying this uppermost intervalare 181 feet of fossiliferouslimestone bearing a shelly fauna similar to that in the upper part of theLombard. This macrofossil-rich sequence stands in sharp contrast to theunderlying claystones, siltstones, and shales whichcharacterize most of the Railroad 248 Canyon section, and indicatesa significant change in depositional environment. Conodonts and brachiopods diagnostic of early to late Chesterian deposition occur in the fossiliferous RailroadCanyon limestones. On the basis of biostratigraphic and lithostratigraphic relationships the thick, macrofossil-rich intervalnear the top of the Railroad Canyon can be correlated tentativelyto the uppermost shallow water tongue of the Lombard. Middle late Chesterian In middle late Chesterian time (Foraminifera Zone 17,upper part) shoaling was initiatedon the outer cratonic platform, probably as a result of tectonic upliftor cessation of subsidence. This change is marked by the return ofcarbonate bank deposition and upbuilding in the samearea as the previous Scott Peak bank complex (plate 4-E). The contact between the deep water South Creek deposits and overlying SurrettCanyon bank deposits is covered, but the transition is recognizedas a progressive increase in mud mound and Waulsortian mud mounddeposition (P.E. Isaacson, personal communication,198). Initial deposition of the Surrett Canyon banklimestones coincides in time with the final stagesof Lombard deposition (Fig 49). Westward shoaling, possibly relatedto rates of subsidence progressively decreasing from east to west,is implied by progradat ion of the uppermost fossiliferouswackestone-packstone tongue in the Lombard from the Snowcresttrough through the Railroad Canyon area. Shoaling in the present day Snowcrest Range area climaxed at this timeas a sequence of thick, 249 fossiliferous packstories whichpass upward into fossiliferous and slightly oolitic grainstones, whichat a few places are overlain by lenticular limestone lithoclastconglomerates. These deposits reflect deposition in a shallow, turbulent,subtidal platform environment with local carbonate bar andsubtidal channel development. Regionally, this shoaling eventmay coincide with the shoalirtg event occurring on the outer platformat the beginning of Surrett Canyon deposit ion. As buildup of the SurrettCanyon bank progressed, and/er uplift occurred on the outercratonic platform, silling at the mouth of the Snowcrest troughwas reinitiated. Consequently, a vertically stratified water columnwas established in the basin, creating anoxic benthos conditions inimicalto epifaunal and infaunal taxa. In addition to pronouncedchanges occurring on the outer platform and within the Snowcrest trough,tectonic instability external to the depositional basin resultedin an accelerated influx of terrigenous clastic material. This acute alteration of the depositional environment is recordedin the thick, calcareous shale sequence overlying the thicker fossiliferouswackestone-packstone sequence (tongues IVS-VIS) of theupper part of the Lombard (plate 3). While outer platform subsidencehad substantially slowed or ceased, and/or started risingslowly, and tectonic instability in the region north or northeast of thebasin was renewed, the tectonic character within the Snowcresttrough at this time is uncertain. The faunal similarity of theupper Lombard shales to the spicular lime mudstones in the lowerLombard implies the return ofan environment somewhere in the basin conduciveto the occurrence of sponges in excess of other faunal elements. Textural dissimilarities, such as the widespread absence ofbioturbation, presence of pyrite, and local presence of abundant phosphaticpellets, implies sedimentation in a unique Lombard depositionalenvironment. Two models can be hypothesized to explain theorigin of the calcareous shales. In the first model, subsidence in theSnowcrest trough remained slow or stopped, anda shallow, stagnant sea developed behind the submerged carbonate sillto the west. ThE fetch in the basin may have been significantlyreduced by falling sea level or tectonic elevation of the basin, limitingthe depth of normal wave base associated with wind-drivenwaves. If the sea was essentially stagnant and anoxic throughout, carbonateproduction would tend to be inhibited or significantly decreased(Enos, 1983). The time span represented by thecalcareous shales and overlying dolomitic lime mudstones is unknown,but is believed to have been relatively short becauselate and latest Chesterian brachiopods (Foraminifera Zones middle18 to 19) occur in the overlying Conover Ranch Formation,and early to late Chesterian corals occur near the top of theunderlying, youngest shallow water Lombard tongue (tongue VIS; C. F. Keyand U.J. Sando, personal communication, 198). ccumulat ion of a 148 foot thick shale sequence over a short time period wouldnecessitate a moderate to rapid sedimentation rate whichseems unlikely in a stagnant sea. The bioclast assemblage, dominatedby sponge spicules, was possibly transported in suspensioninto the shallow sea from the 251 carbonate bank or some other,unrecognized source by weak (damped) tidal currentsor wind-generated waves. Transportation of the dense, detrital(?) phosphaticpellets is more difficult to rationalize, however, if currentsand waves in the restrictedsea were so weak and attenuated that thewater had become nearly stagnant. The second, favored, modelinvolves subsidence of the Snowcrest trough behind thecarbonate bank and consequent deposition in a deep, verticallystratified basin. Subsidence in excess of sedimentation in the axialpart of the Snowcrest trough would cause development ofanoxic bottom water conditions in the deepest parts of the basin,below the pycnocline, and rapid migration of the fossiliferouswackestone-packestone lithotope toward the bank and the troughmargins (plate 4-E). Depth and associated anaerobicityare envisioned as the primary factors responsible for the lack ofbenthic infauna and epifauna in the calcareous shales. Greater subsidence than duringany previous period of Lombard depositionadditionally explains the development of this unique Lombardlithofacies. The uppermost Lombard atthe head of the trough, in the Bridger Range area, ischaracterized by fossiliferous wackestones and packstones interbedded with lime mudstones. The wackestone and packstone beds consistpredominantly of pelagic foraminifers, sponge spicules or brachiopodspines, and scarce solitary corals. Late tThesterian conodonts also occur in these beds(Suthrie, 1984). Thus, they may be approximatelycorrelative in time with the fossiliferous wackestone-packstone to calcareous shaletransition 252 in the upper Lombard in the studyarea. The disconformity between the Lombardand the Conover Ranch in the Bridger Rangearea, however, does not permit a reliable correlation with either theshale or the overlying dolomitic lime m*idstone lithofacies because theamount of missing section is unknown. The calcareous shale and dolomitic limemudetone lithofacies also are missing in the BlacktailMountains, .just north of the study area, and fartherwest at Railroad Canyon (Beaverhead Mountains; fig. 1). Fossiliferous wackestones and packetones with interbedded lime mudstones and siltylime mudstones dominate the upper part of the Lombard at both locations (Pecora,1981; Wardlaw and Pecora, 1985). The Lombard-Conover Ranch contact at Sheep Creek Canyon may be unconformable,as previously established. Several specimens of Duncanoperaep., occur here in a fossiliferous wackestone bed 37 feet below the base ofthe Conover Ranch. This coral is diagnostic of CoralZone VB, indicating late Chesterian deposition (ForaminiferaZone 17 to middle 18; W. J. Sando, written communication,1985). Thus, the beds above this may correlate in time withthe calcareous shales. The amount of Lombard section missingat the Lombard-Conover Ranch contact at Clover Meadow, in thenorth-central Gravelly Range, is unknown. As at Sheep Creek Canyon, theuppermost Lombard is made up of fossiliferouswackestones and packstones of Chesterian age. While correlation to the uppermostLombard beds in the Bridger and Gravell Ranges may not be tenable, correlationof the calcareous shale sequence withthe uppermost Lombard rocks at Sheep Creek Canyon, RailroadCanyon, and the Bridger Rangearea 253 has merit. If the contacts at Sheep CreekCanyon and Clover Meadow are conformable the shales may have beendeposited within a narrow, deep, anoxic part of the basin,approximately centered in the study area. Conversely, the shales may have been widespread within the trough, but subsequentlyremoved by post-Lombard, pre-Conover Ranch uplift anderosion. Post-Lombard, pre-Conover Ranch uplift and erosion,or unrecognized thrust faulting is inferred at the southwestern end of thestudy area (Red Rock River section); the absence of shaleshere, therefore, is not interpreted to be the result ofnon-deposition. The deep water modelmay also facilitate moderate sedimentation rates, in contrast tothe shallow, stagnant sea model. In a deep, vertically stratifiedbasin the uppermost part of the water column could be welloxygenated and support an abundant planktonic, carbonate-secretingfauna. Carbonate detritus would also be carried intothe axial parts of the trough from the peripheral shallow waterareas and/or the carbonate bank complex by regular tidal currents. The fine bioclast assemblage in the shales implies attenuatedwaves and currents incapable of transporting larger bioclasticdebris, although these coarser grains may have been deposited from suspensionor bedload somewhere between the shallow and deepwater area. If the greater depth of the sea can be related togreater areal trough dimensions, then wind-generated waves resultingfrom a larger fetch may have been able to transport coarser debris greater distances; thismay explain the origin of detritalphophatic pellets in the shales. 254 The detrital phosphaticpellets suggest periodic phosphcirite precipitation on the northern(?)end of the bank complex associated with south-southeastward-directedupwelling in the miogeosyncline (upwelling induced by west-southwestblowing paleotrade winds). The pellets in the shalesmay reflect seasonal storms which caused disaggregation of the phosphaticnodules or pellets on the bank and subsequent transport into thedeep parts of the Snowcrest trough. In the final stages ofLombard deposition, basin subsidence slowed, sea level fell, and/orcirculation in the platform sea improved slightly, causingdeepening and/or destabilization of the pycnocline (plate 4-E). Dysaerobic bottom conditions progressively replaced anoxic bottom conditionsas documented in the gradational transition from the azoic, laminatedcalcareous shale to the bioturbated dolomitic limemudstone lithofacies (plate 3). The abundant infauna connoted bywidespread bioturbat ion, and the absence of any carbonate-secretingbenthic fauna suggest dysaerobic conditions prevailed in thebasin throughout the remainder of Lombard deposition. The paucity of bioclasts, nowhereexceeding ten percent of the total constituents, suggests the developmentof a stressful environment whichinhibited habitation of carbonate-secreting organisms. On the other hand, dissolutionor destruction of most bioclasticmaterial by chemical and/or bioloqicl processes may have resulted from slowsedimentation rates and prolonged exposure at thesediment-water interface. Coincident with the initiationof lime mudstone deposition, the influx of clastic material into the trough decreased, implyingthat uplift in the extrabasinalarea had slowed or ceased, or that the 255 sediment was diverted elsewhere. Dolomitization of the lime rnudstones followed bioturbation,as discussed in an earlier section. Uplift in the northeasternpart of the trough or substantial shoaling may have facilitatedthe development of a meteoric mixing system which induced dolomitizationof these rocks. Rapid regression of the sea at the endof Heath deposition in the Big Snowy trough (Maughan,11384) may correspondin time with this dolomitization event (plate 4-F). Evidence of supratidalor intertidal deposition is not present in these rocks. Deposition of the rocks of this lithofacies, therefore, is inferred tohave occurred in a dysaerobic carbonate sea of shallow to intermediate waterdepth. P shallow, fossiliferous limestone belt probably continuedto develop along the basin margins. The areal extent of depositionof the dolomitic lime mudetone lithofacies is unknown. The dolomitic lime mudstone lithofacies has neither beenrecognized nor reported elsewhere in southwestern Montana. Complete withdrawl of the Lombardsea prior to Conover Ranchdeposition is implied by the unconformity between these two units whichis pervasive in most of the study area. Thus, the originalarea of dysaerobic lime mudstone sedimentation may be falselyrepresented by the present-day restricted distribution of thislithofacies. On the other hand, these rocks may have been depositedin a narrow, slightly deeper part of the trough, flanked byfossiliferous limestones laid down in shallower water abovewave base. 256 Latest late Chesterian Transgression of the sea continued into Pennsylvaniantime in the Wyoming basin (Sando, 1976). The close of Lombard and Heath deposition in the Snowcrest and Big Snowytroughs, respectively, is constrained to a late to latest Chesterianage, however, by biostratigraphic data. Regression of the sea must, therefore, be the result of nearly simultaneous uplift in theBig Snowy and Snowcrest troughs (fig. 49). The Lombard and Conover Ranchare conformable in the Tendoy Mountains (Sando et al.,1985; Wardlaw and Pecora, 1985). Thus, the sea must have withdrawnto some position midway between the study area and the presentday Tendoy Mountains area near the close of late Chesterjan time (ForaminiferaZone 18, middle to upper part; fig. 49) (plate4-G). Deposition of cross-laminated sandy siltstones and thin- tomedium-bedded limestones, which characterize theuppermost Railroad Canyon Formation (Wardlaw and Pecora, 1985),probably began or was continuing at this time. Renewed subsidence in the basin, continued rise in regionalsea level, and/or brief subsidence of the Surrett Canyon bank complexsubsequently occurred, initiating deposition and onlap of the transgressiveConover Ranch on the eroded Lombard deposits (C. F. Key,in preparation, 1985). 257 PETROLEUM POTENT I L Prior to the late 1960's, few workers focused on the petroleum potential of the Lombard Limestone (Big Snowy Formation). In one of the earliest investigations dealing with both the Paleozoic and Mesozoic rocks in southwesternmost Montana, Scholten (1.967) alluded to the poor oil potential of the region because of the long, complicated tectonic history. Mid- to Late-Cretaceous uplift and subsequent exposure of pre-Cretaceous source rocks along the flanks of the major ant iclinoria (fig. 8) were the main reasons for this pessimistic outlook. Scholten (1967) concluded "...it may be expected that most, or all, hydrocarbons migrated to the surface at that time and were transported by surface waters or dissipated into the air." Thirty-one wildcat wells have been drilled in southwestern Montana as of 1983 (Perry at al., 1983). To date, none have produced commercial quantities of oil or gas, and most have reported only minor shows of either. Two stratigraphic holeswere drilled at the northern end of the study area in 1984 (fig. 54); results of these wells presently are not available (Pat McGraw, personal communication, 1985; these wells are U.S. Ellis Estate *1 and *2, T. 8 S.,R. 5 W.). These are the only two wells which test the Snowcrest trend. Well locations near the study area are illustrated on Figure 54. Detailed geochemical analyses of the Lombard (Big Snowy Formation) in southwestern Montana have concentrated on sample collections from surface exposures on the Tendoy thrust sheet S. Lu LEGEND ...v DILLON asssav., U .,is.i Isss$I.si IALSV rI s* .tI: dvp ( Pit. .tI: .st,s*Is.phIs INsult _g1) 1 I V p...,vuIi J A t Mat.' Ibway I I) aNi -s.esstsvy,.sd '-'.4 / A '-.,( PrI.ItIe. i..d S.' 510 WIll5 P.essi IsiltS fU*SI SLAIN 0 / VII £USISI p1.1 aISVOSI a ( 0., ( V ; 'U a MONT ANt. \I 4U* iia DILl IIt S I. a S J. LINt. ' N N $ LII .S$51 Figure 54. Map of southw.sternmost Montana showing abandoned well locations and surface sample collectionlocations for source rock analyses. N) 259 (Swetland et al., 1978; Perry et al., 1981, 1983). Geochemical data east of the overthrust belt are sparse. In a petroleum source beds study of the northern Rocky Mountain region, Swet land and others (1978) collected five surface samples from the lower part of the Lombard (lime mudetone lithofacies) at Clover Divide (Blacktail Deer Creek Road; their locality 8), which yielded a total organic carbon value of 1.8 percent. No other geochemical analyses were completed. Recent work in the Snowcrest-Greenhorn-Blacktail area has provided new impetus for reconsideration of the petroleum potential of the Lombard Limestone in southwesternmost Montana. analyses of major stratigraphic and structural trends suggest the likely presence of a deep-seated, northeast-trending sub-Snowcrest Range thrust fault which soles or underlies the subordinate Snowcrest and Greenhorn thrust faults (Perry et al., 1981, 1983; Kulik, 1984). Five points of evidence are presented by Perry and others (1983) which substantiate the existence of this major Laramide thrust fault. Gravity, aeromagnetic, structural, and stratigraphic data further suggest that the inferred sub-Snowcrest Range fault extends westward beneath the Tendoy and Medicine Lodge thrust sheets (fig. 5). The significance of a major sub-Snowerest Range detachment fault lies not only in the possibility that potential petroleum source rocks are buried beneath the leading edge of the southwestern Montana overthrust belt, but also that thesesame units may presently exist at depth in the autochthonous (footwall) block east of the overthrust belt (fig. 56). If the drag structure suggested in Figure 36 exists, and if the basement rocks and 12O 1IT'IO 11230 4, 11220 4 4 . Anlone EXPLANATION p \ I 4 hol.. with ssShOws '0.11 I + Oil oe g.e w.ft-- 4 .. D,y hell 'f \ \ 7 .gC? Sh.0 Oil 4 .O' 34.-IS ) 4440' .il . ri.iCI.icii&i \ .,, -S . I ' S.c Novices levIS-- )% - 4 S.c - Osshd wk.i icf.u.d. 4' Lima ..., 4',, hs$chu,ss eu ØOwuIth,ows CENTENNIAL. C;'.. aO4. Side \ VIA.' FAULT C.n..... Am. Que*, t..ma P.., C'..k. S*Sifllflt thiu5$ S.ull-- 5s.s. ...-.,.f4 .i Mos.d* P.4.v.I 2S4 DotI.d wluevl lnterr.d. 9-31 "s.. 4 /4 SewI.sthOsippsv plOts S. '%V.S - D.techm.sI Ihivet f5lt-- os' ANA 10 Eason .wt.sth cii vppsc plate )l ' Amoe I Msysvs-Psdsvsl SViOWIufl I Unul IDAHO S.. 'i.isng P.d.;eI ---S 4430' C5'5.---5. / STUSY SCALE '9rI .5.. C WYOMING 0 5 KILOMETEPS IDAHO .5 ci I sits ._ Figure 55. t3eneralized tectonic map of southwest.rnmost Montana showing position of inferred ub-Snowcrest Range thrust fault and relationship with Tendoy and Medicine Lodge thrust sheets (from Perry et al., 19B3). Line B'B' corresponds to Figure 56. 261 NW SE SAGE CREEK SUB --SNOWCRESI TERTIARY BASIN RANGE THRUST / SNOWCREST STRUCTURAL // 8 TERRANE _/ +2'----/ i : +1 MESOZOIC SL SL 2 (I, Iu -2 -I -4 _f. 0 ''-'"r"? ''-'r ''''' -6 4 1._-r t_#'..!,PRECAMBRIAN"'-.I,I%--I #% . I_#l' % __,_' I , -' -B < -10 #_l_ !'-'.-' !r I i, o 5 MILES I I . . . o 5 KILOMETERS NO VERTICAL EXAGGERATION Figur. 56. Hypothetical cross cect ion B-B' through Snowcrest t.rran (frce Perry et ci., 1983) Line of sct ion shown on Figure 55. bracketing Mission Canyon and Conover Ranch units provide adequate seals, and if the thermal conditionsare right, then an attractive oil play may be present. Surface samples were collected by the author atseven locations in the Snowcrest Range (fig. 4; Appendix C). Most of the samples were obtained from the lime mudstone lithofaciesof the lower part of the Lombard. Four samples were collected in the calcareous shale lithofacies andone sample was taken in the uppermost exposed fossiliferous wackestone-packstone 1 ithofacies bed at Sunset Peak; this sample is included with the limemudstone lithofacies in the following discussion. The samples were analyzed for thermal maturation, total organic carbon,extractable hydrocarbons (bitumens), and kerogen content and type(s) (table 3). Rock-eval pyrolysis and gas chromotography analyseswere additionally completed on promising samples (see table 4 and Appendix D). All maturity ratings in the subsequent discussion are based on the carbonate standards used by Tenneco Oil Company (used with permission); these standardsare listed on Figure 7. Results and interpretation Vitrinite reflectance values of ø.47Ro to ø.87Ro obtained from rocks of the lime mudstone and calcareous shale lithofaciessuggest that the organic material is transitionalor mature with respect to oil generation. Cross-referencing these thermal maturity indices with spore/pollen color values (3 to 3+),however, indicate that all of the Lombard rocks analyzedare thermally mature (see Table 3). The low vitrinite values in several ofthe samples are the result of SOURCE ROCK EURLW3T ION OATS - LOflUARU LIIIESIDHE Sa.p1eSpore Uit. NC bC INR Hunic Land Cx liar. Cx Sapropelic Renarks B Lith.Color Ro X ppn I K ppn K pp., 1 pp., K pp.t 1 Ui 3 0.62 0.31 0 50 10558 0 0 0 0 32 992 Fresh contanlnatlon 2 LII 3 0.68 0.36 0 10 4 144 0 0 0 0 86 3096 treoh contatilnetion 3 UI 3 0.75 0.31 0 - Too oparee 4 UI 3 0.79 0.19 0-- - Too eparee SUi 3 0.76 0.81 0 6 4 336 2 168 0 0 08 7392 rreah conta,,tnatlon LII 3 0.67 1 .06 980 6 22120 0 0 0 92 9752Fresh conta.,ln.t*an 1UI 3 - 0.67 110 760 4 6 660 2 220 0 0 88 9688 UI 0 3 -- 0.31 0 10 0 0 2 62 II 0 00 2180 9 UI 3 -- 0.46 0 10 0 0 0 368 0 0 82 3772 10 reah contatUnatlon UI 3 0.58 0.91 980 6 2 102 I 361 0 0 88 8008 11 CS Freeb contaninatlon 3 0.74 1.691690 12 2318 4 636 0 0 82 13038 12 Ui 3. 0.87 0.71 2050 10 2 142 2 142 0 0 86 6106 13 UI 3 0.83 0.23 660 - if UI finest barren 3 0.6? 0.661270 18 6 396 I 261 0 0 72 1752Fresh contanination 15 CS 3 0.17 1.393160 3 4 556 4 556 0 0 04 11676Fresh centaninotian 16 CS 3 0.50 1.39 2300 22 2278 2 278 0 0 74 10286 Fresh contaninetion 1? UI 3 0.82 0.23 0 18 2 16 -0 . 0 0 0 80 1840 18 UI 3 0.81 0.39 0 - Too sparse 19 UI 3 0.82 0.16 0 - Too sparse 20 Ui 3 0.51 0.15 0 - Too sparse; Contan. 21 UI 3 0.75 0.21 0 - - Too spores 22 UI 3 0.73 - 0.22 0 - - Too sparse Sample &Lith.: Sample number (seeAppendix C) INR %; Inertinite content Lithofacies; LII Lime mudstone Humic; CS Calcareous shale Humic kerogen content Vit. Rog Vitrinite reflectance Land Ex: Land exiriite conterst Mar. Ex: bC %: Total organic carbon (weightpercent of rock) Marine exinite content HC ppm: Extractable hydrocarbons Sapropelic: Sapropelic kerogencontent Table 3. Data obtainedfrom source rockevaluation of Lombard Limestone samples. Samples analyzed at Tenneco OilLaboratories. o. (A) RESULTS orROCK-EWIL PYROLYSIS Sanple Tnax Si S2 S3 PT PC* TOC Hdro Oxy ft Lith ( C) (ng/g)(ng/g)(ng/g) (X) IndexIndex 6 UI 433 0.15 3.02 OfO 0.05 0.26 1.06 281 3? 7 UI 430 tL26 3.6? O50 0.0? 0.32 110 333 is 11Cs 426 0..2f 5.98 0.59 004 0.51 1.59 376 37 12 In 430 0.09 1.7? 0.19 0.050.15 0.71 219 69 ifUI 431 0.12 2.11 0.35 0.05tLl8 0.66 324 53 15 CS 42? 029 5.61 0.50 0.05 0.19 1.39 403 35 16 CS 426 0.20 1.72 0.48 0.04 0.41 1.39 339 34 Explanation of column headings: Sample: Sample number (see Appendix C) Lithofacies: Lt't = Lime mudstone; CS = Calcareous shale Tmax: Temperature index, degrees C Si: Free hydrocarbons, mg HC/g of rock $2: Residual hydrocarbon potential (mg HC/g ofrock) S3: CO produced from kerogen pyrolysis (mg CO /g ofrock) P1: St/SI + $2 (transformation index) PC*: 0.083 (Si + $2) TOC: Total organic carbon, weight percent Hyd md: Hydrogen index, mg HC/g organic carbon Oxy md: Oxygen index, mg CO /g organic carbon Table 4. Results of Rc'ck-eval pyrcilysis on Lombard Limestone samples. Analyses made at Tenneco Oil Laboratories. 265 STANDARDS FOR HYDROCARBON SOURCE-ROCK EVALUATIONS Maturation Level Spore Color Index Vitrinite Ro limnature 1 Yellow -Stains) 0.55 Gas Transitional 2 Yellow Brown) 0.55 - 0.7 Gas & Minor Oil * Mature 3Brown) 0.7 - 1.0 Gas & Oil Very Mature 4 Dark Brown) 1.0 - 1.5 Wet Gas/Condensate Advanced 5 Dk.Brown to Black) l.5 Gas Total Organic Carbon (T.O.C.) (S of Rock Shales Carbonates Poor 0.5 0.2 Fair 0.5 - 1.0 0.2 - 0.5 Rich 1.0 - 2.0 0.5 - 1.0 Very Rich '2.0 1.0 Extractable Hydrocarbons (H.C.) (ppm, of Rock) Shales Carbonates Poor "500 4100 Fair 500 - 1000 100 -500 Rich 1000 - 2000 500 - 1000 Very Rich "2000 "1000 Sapropelic (S of T.0.C.) Poor Primary Oil- Migration Potential "40 Good Primary Oil- Migration Potential '40 Kerogen ContentJHumic, Exinite, Saorooelic) (oom.of Rock Poor '2000 Fair 2000 - 5000 Rich 5000 - 10,000 Very Rich '10,000 Inertinite"(INR.) (S ofT.0.C.) Generates no hydrocarbons. Analyzed due to Inclusion in total organic carbon analysis. Figure 57. List of standards for petroleum source rock analyses used in this report (used with permission of Tenneco 011 Company). 266 fresh kerogen contamination (J.H. Ruff in, written communication, 198). The spore/pollen color values, therefore, are considered to more accurately reflect the thermal maturation of the Lombard rocks. Analysis of these samples by pyrolysis techniques also suggests moderate burial and moderate temperatures. As shown on Table 4, S. values (fraction of the original organic matter available for hydrocarbon generation) exceed 5, values (fraction of the original organic matter already transformed to hydrocarbons) in all cases. Increased burial and/or elevated temperatures cause 5, values to increase at the expense of decreasing S. values (Barker, 1980). Thus, the marked dichotomy between S and S, values, which range from (S.:S,) 14:1 to 24:1, argue against deep burial and/orexposure to high temperatures. The total organic carbon content of these rocks ranges from poor to very rich based on the carbonate standard, but most display a sufficient organic richness for source bed potential. Comparison of the average total organic carbon content in the lime mudstones (average TOC = 0.48 percent) and calcareous shales (average bC = 1.46 percent), however, revealsa striking difference. The latter rocks contain, on average, almost three times the amount of total organic carbon found in the former rocks. In congruence with the high total organic carbon values in the calcareous shales, the hydrocarbon content in the shalesis very rich, averaging 2,383 ppm. The extractable hydrocarbon content in the lime mudstone, however, is generallyzero, although a few 267 samples contain enough bitumens to assign thema rich to very rich classification (table 3). Spore/pollen color and vitri/nite reflectance values indicate that the Lombard has not experiencedar unfavorably high thermal history. The low hydrocarbon content, therefore, is probably the result of oxidizing conditionsat the surface (S. H. Ruff in, written communication, 1985). Moderate to high total organic carbon values in rocks withno measurable hydrocarbons substantiate this hypothesis (table 3). Sapropelic (amorphous) kerogen is dominant, followed by humic and land exinite fractions, respectively. Eight of the fourteen samples containing measurable kerogenare rich or very rich with respect to sapropelic kerogen. The humic and land exinite fractions are insignificant in quantity, makingup less than ten percent of the total kerogen content in all butone sample (table 3). Sapropelic kerogen is chiefly derived from biodegradationof the rich lipid and protein residues from theexinite fraction (primarily planktonic marine algae) (3.H. Ruff in, written communication, 1985; Tissot and Welte, 1978). This hydrogen-rich kerogen is a major source of oilupon subjection to thermal catagenesis. minimum concentration of 40 percent sapropelic matter is required to generate enough oil to initiateprimary migration. The sapropelic kerogen content, which generally exceeds 80 percent in the Lombard carbonates, signifiesthat sufficient quantities of sapropelic matterare present to induce this process. Calculation of the hydrogen andoxygen indices obtained from pyrolysis analyses suggest thatsome of the organic matter (kerogen) in the Lombard hasa continental origin. There is a good correlation between the hydrogen index and atomic H/U ratio, and between the oxygen index and atomic 0/C ratio, respectively. This correlation facilitates the plotting of hydrogen index values against oxygen index values on a van Krevelen diagram (Tissot and Welte, 1978). The Lombard values plot midway between the type-tI and type-Ill kerogen evolution paths (fig. 58). TypeII kerogen is dominated by sapropelic matter, predominantly derived from marine planktonic matter deposited in a reducing environment. Type-Ill kerogen is derived chiefly from continental plants and, therefore, contains substantially more humic matter than type-Il kerogen (Tissot and Welte, 1978). The samples from both Lombard lithofacies plot closer to the type-lI kerogen evolution path than to the type-Ill path, suggesting a predominance of marine organic matter input. In addition, the calcareous shale lithofacies kerogen values plot closer to the type-U evolution path than the lime mudetone lithofacies values (fig. 58). This may reflect deposition farther offshore, reduced input of continental plant material,or loss of the continental plant matter close to shore. The presence of sufficient humic material to slightly skew the Lombard kerogen field toward the type-Ill evolution pathmay be the result of the epicontinental position of the Lombard sea. The thermal maturity, total organic carbon content, and hydrocarbon content indicate that these rockswere rich to very rich oil source rocks at some time when theywere sufficiently buried Ci.H. Ruff in, written communication, 1985). Determination of the genetic potential of the samples, however, suggests thatthe capacity of the Lombard to generate additional hydrocarbons is 269 £900 750 450I:TI 150 -.----_*TTT A. 0 50. iào 150. -+ OXYGEN INDEX (nCOjg crg. C) X Caicareous Shale Lime Mudstone Figure 58. Classification of source rock keroqen. types based on hydrogen and oxygen indices. Kerogen evolution paths f roe Tissot and welt. (1984). Lombard samples plot midway between Type-li and Type-I!! kerogen evolut ion paths, suggesting thepresence of both sapropelic and humic types of kerogen. See Table 4 for raw data. 270 moderate for both lithofacies, based on the standards given by Tissot and Welte (1978; fig. 59). The average genetic potential for the lime mudstones is 2.56 kg HC/ton of rock, while the calcareous shales yield an average of 5.16 kg HC/ton of rock (fig. 59). On the basis of these values, the Lombard should be taken to have at least a moderate source rock potential. 271 GENETIC POTENT IL Sample Lithofacies Si Se Si + 52 Number Cmg/g) (mglg) (kg/t) 6 Limemudst. 0.15 3.02 2.88 7 Limemudst. 0.26 3.67 3.57 11 Caic.shale 0.24 5.98 5.65 12 Limemudst. 0.09 1.17 1.69 14 Limemudst. 0.12 2.24 2.05 15 Caic.shale 0.29 5.61 5.36 16 Caic.shale 0.20 4.72 4.47 Si: Free hydrocarbons, mg HC/g of rock 52: Residual hydrocarbon potential, mg HC/g of rock Si + S2: Genetic potential, kg HC/ton of rock Grade classification (from Tissot and Welte, 1978) (2 kg/t ((2000 ppm) = no oil; some gas potential 2 to 6 kg/t (2000-6000 ppm)= moderate source rock >6 kg/t (>6000 ppm) = good source rock Figure 59. Evaluation of genetic potential of selected samples from the Lombard Limestone. 272 CONCLUS I ONS The Kibbey Formation and Lombard Limestone reflect middle Meramecian thorugh late Chesterian deposition in an intermittently silled trough in southwestern Montana. Kibbey sedimentation was initiated when the Big Snowy sea transgressed across the Mission Canyon karst plain in response to subsidence of the inner cratonic platform and/or eustatic rise in sea level in middle Meramecian time. The Kibbey Formation is divisible into two lithofacies, or units. The lower unit consists predominantly of silty and sandy dolostones deposited on an upper intertidal to lower supratidal (mud flat) environment. Calcite- and dolomite-cemented quartz arenites, deposited in a lower shoreface to lower intertidal (sand flat) environment, constitute the upper unit of the Kibbey. Lombard sedimentation began at the study area in early late Meramecian time as a result of (1) rapid subsidence of the southwestern half of the Snowcrest trough,(2) the cessation of clastic input into the basin, and/or (3) northeastward migration of the Kibbey shoreface. Four lithofacies are recognized in the Lombard in the Snowcrest Range (plate 3). These four lithofacies, in ascending stratigraphic order, are: (1) the lime mudstone lithofacies, dominated by sponge spicules and ostracode debris, reflecting quiet, dysaerobic marine conditions below normal wave base;(2) fossiliferous wackestone-packstone 1 ithofacies, containing a diverse and abundant shelly fauna representing agitated, well oxygenated, silt-free marine conditions above normal wave base; (3) calcareous shale lithofacies characterized by detrital phosphatic 273 pellet-rich intervals, a paucity of bioclastic debris, and no bioturbation, indicative of deep, anoxic marine sedimentation below the pycnocline; and (4) the dolomitic lime mudstone lithofacies, reflecting slightly increased oxygen levels at the bottom which allowed benthic infauna to thrive, but inhibited establishment of a shelly fauna. nalysis of the intertonguing relationships of the lime mudstone and fossiliferous wackestone-packstone lithofacies, and isopach data of the Lombard, suggest that subsidence in the southwestern half of the Snowcrest trough exceeded that in the northeastern half throughout most of Lombard time (figs. 52, 53). Correlation of the Kibbey and Lombard lithofacies with time-equivalent units to the west and east reveals the significant impact of differential episodic subsidence of the inner and outer cratonic platforms on the type and rate of sedimentation. Seven major tectono-sedimentary events are recognized in the southwestern Montana and east-central Idaho region: 1. Late middle Meramecian: Kibbey Formation deposited in the subsiding Snowcrest trough behind an upbuildirug carbonate bank complex (Scott Peak Formation) on the outer cratonic platform (plate 4-a). 2. Late Meramecian: Continued upbuilding of the bank and/or tectonic elevation of the outer cratonic platform produced a moderate sill at the mouth of the Snowcrest trough (plate 274 4-B). Episodic differential sedimentation at the northeastern end of the trough. promoted cyclic progradation and retrogradation of the shallow water limestones (fossiliferous wackestone-packstone lithofacies) over deep water lirnestones (lime rnudstone lithofacies). Subsidence in the southwestern part of the trough continued to exceed sedimentation, resulting in deposition of a thick lime mudstone lithofacies sequence. 3. Early Chesterian Rapid subsidence of the outer cratonic platform caused drowning of the bank complex (Scott Peak Formation) and initiation of calcareous shale (South Creek Formation) sedimentation in its place (plate 4-C). Decreased subsidence rates in the Snowcrest trough combining with improved basin circulation enhanced proliferation of the shallow water shelly fauna. Rapid southwest-directed progradat ion of the fossiliferous wackestone-packstone lithofacies occurred basinwide. Shoaling locally resulted in the development of swamps, which are reflected in the Lombard as thin coal seams. Kibbey and Otter deposition began at this time in central Montana when the Big Snowy sea transgressed over the Lombard arch into the subsiding Big Snowy basin. 4. Early late Chesterian: Slow subsidence rates and ideal conditions for carbonate-secreting epifauna in the trough caused continued progradation of the shallow water limestones 275 at least as far as the present-day southwesternmost Montana area (plate 4-D). Subsidence of the outer cratonic platform continued to exceed sedimentation. 5. Middle late Chesterian: Uplift of the outer cratonic platform promoted re-establishment of a carbonate bank complex (Surrett Canyon Formation), creating a silled basin in the Snowcrest trough (plate 4-E). Rapid subsidence, greater than during previous subsidence events on the inner cratonic platform, and the development of anoxic bottom conditions in the central and southwestern parts of the Snowcrest trough resulted in the deposition of calcareous shale. Shallow water limestones were deposited in the northeastern part of the trough where sedimentation was slightly greater or equal to subsidence. 6. Middle late Chesterian: Decreased subsidence and/or slight uplift of the southwestern and central parts of the Snowcrest trough, and destabilization of the pycnocline caused a change in bottom conditions permitting the return of a benthic infauna. The carbonate bank at the mouth of the trough continued to act as a submerged sill, however, causing dysaerobic benthjc conditions inimical to the development ofa shelly fauna in the present-day Snowcrest Range area (plate 4-F). The gradational transition from the calcareous shale to the dolomitic lime mudetone lithofacies records this progressive change in deposit ional environment. In the 276 vicinity of the Montana-Idaho border shallow water conditions prevailed, extending westward to the bank complex on the outer cratonic platform (plate 4-F). 7. Latest late Chesterian: Regional uplift in central and southwestern Montana caused complete withdrawl of the Big Snowy sea to a position between the present-day Snowcrest Range area and Montana-Idaho border. Clastic material shed from the elevated landmass to the east was deposited in shallow lagoons and estuaries in southwesternmost Montana (Conover Ranch Formation; plate 4-9). Subsequent subsidence in the trough resulted in overstepping of the slightly(?) eroded Lombard by the Conover Ranch as thesea transgressed to the east. The lime rnudstone and calcareous shale lithofacies of the Lombard in the Snowcrest Range displaya moderate or good petroleum source rock potential, based on geochemical analyses. Favorable traps for hydrocarbon accumulation may be present in southwesternmost Montana as a result of structural overprinting of Laramide and Sevier thrust faulting, and in the Snowcrest region in association with the inferred sub-Snowcrest Range thrust fault. Such traps at depth, which incorporate Lombard raudstones and shales may be alluring targets to exploration geologists. 277 BIBLIOGRflPHY Adams, J. E., and Rhodes, M. L., 1960, Dolomitization byseepage refluxion: Amer. Assoc. Petrol. Geol. Bull., V. 44, p. 1912-1920. Ballard, W. W., 1961, Sedimentary petrology of post-Madison pre-Kootenai rock, west flank of the Little Belt Mountains Montana: unpublished Ph.D. thesis, Univ. of Texas, Austin. Barker, Cohn, 1980, Source rocks: in Organic Geochemistry in petroleum exploration, Amer. Assoc. Petrol. Geol., Short Course 10, 159 p. Bathurst, R.S. C., 1975, Carbonate sediments and their diagenesis: Elsevier, Amsterdam, 658p. Berner, R. A., 1970, Sedimentary pyrite formation: Amer. Jour. Sci., V. 268,p. 1-23. Brewster, D. p., 1984, Biostratigraphy and depositional history of the Big Snowy and Amsden Formations (Carboniferous) in southwestern Montana: unpub. M.S. thesis, Indiana Univ., 164 p. Blake, 0. D., 1959, Big Snowy stratigraphy in thearea .adjacent to the Rocky Mountain front: Billings Geol. Soc. Guidebook, 10th Ann. Fid. Conf.,p. 64-68. Byers, C. U.,1977, Biofacies patterns in euxinic basins: general model: jCook, H. E., and Enos, Paul (eds.), Deep water carbonate environments, Soc. Econ. Paleo. Miner., Spec. Pub. 25,p. 5-17. Campbell, C. V., 1967, Laminae, Lamina set, bed, and bedset: Sedimentology, V. 8,p. 7-26. Colhinson, 3. 0., and Thompson, 0. B.,1982, Sedimentary structures: George Allen & Unwin, Ltd., London, 194p. Craig, L. C.,1972, Mississippian system: jGeological atlas of the Rocky Mountain region, Rocky Mtn. Assoc. Geol.., Denver, Cob., p.100-110. Davies, S.R.,1970, Algal-laminated sediments, western Australia: Logan, B.U. (ed.), Carbonate sediments and enviroments, Shark Bay, Australia, Amer. Assoc. Petrol. Geol., Mem. 13,p. 169-205. Davis, L. E.,1983, Conodont biostratigraphy of the Alaska Bench Formation, central Montana: Geol. Soc. Amer., Abstracts with Programs, V.15, n.5, p. 410. 278 deLaubenfels, 11. W., 1955, Porifera: inMoore, R.C. (ed.), Treatise on invertebrate paleontology: part E, Geol. Soc. Amer., Univ. Kansas Press, Lawrence, Kansas, 122 p. Dutro, J. 1., Jr., Sando, W. J., and Skipp, Betty, 1984, The Mississippian-Pennsylvanian boundary in the northern Rocky Mountains area of the United States: Sutherland, P.K. and Manger, U. L.(eds.), Biostratigraphy, Neuvieme Congres International de Stratigraphie et de Geologie du Carbonifere, Compte Rendu, V. 2, p. 419-427. Dunham, R. 3., 1962, Classification of carbonate rocks according to depositional texture: Ham, U. E.(ed.), Classification of carbonate rocks, Amer. Assoc. Petrol. Geol. Mem. 1, p. 108-121. ______$ and Olson, E. R., 1978, Diagentic dolomite formation related to Paleozoic paleogeography of the Cordilleran miogeocline in Nevada: Geology, V.6,p. 556-539. Easton, U. H., 1962, Carboniferous faunas of central Montana: U. S. Geol. Survey Prof. Paper 348, 124p. Enos, Paul, 1983, Shelf environment:inScholle, P. A., Bebout, D. G., and Cook, C. H.(eds.), Carbonate depositional environments, Amer. Assoc. Petrol. Geol. Memoir 33,p. 267-295. Ettesohn, F. R., and Elam, 1. D., 1985, Defining the natureand location of Late Devonian-Early Mississippian pycnocline in eastern Kentucky: Geol. Soc. Amer. Bull., v. 96,p. 1313-1321. Fanshawe, J. R., 1978, Central Montana tectonics and the Tyler Formation: Folk, R. L., 1962, Spectral subdivisions of limestonetypes: in Ham, W.E. (ed.), Classification of carbonate rocks, Amer. Assoc. Petrol. Geol., Mem. 1, p. 62-84. 1980, Petrology of sedimentary rocks: Austin, Texas, Hemphill Publ. Co., 184p. Freeman1 0. U., 1922, Oil in the Quadrant Formationin Montana: Engineering and Mining Jour.-Press,v.113,p. 825-827. Gardner, L. S., 1939, Revision of Big Snowy Groupin central Montana: Amer. Assoc. Petrol. Geol. Bulletin, V. 43, p. 329-349. Gealy, U. 3., 1933, Geology of the AntonePeak quadrangle, southwestern Montana: unpub. Ph.D thesis, Harvard Univ., 150 p. 279 Goddard, S. N., 1970, Rock-Color chart: U.S. Gaol. Survey., Boulder, Cob.,no pagination. Gordon, Mackenzie, Jr., 1975, Brachiopoda of theAmsden Formation (Mississippian and Pennsylvanian) of Wyoming: U. S. Gaol. Survey Prof. Paper 848-D,p. D1-D86. Guthrie, 6. 5., 1984, Stratigraphy and depositionalenvironment of the Upper Mississippian Big Snowy Group in the Bridger Range, southwestern Montana: unpub. M.S. thesis, Montana State Univ., 105p. Gutschick, R. C., and Sandberg, C. A., 1983, Mississippian continental margins of the conterminous United States: Soc. Econ. Paleo. Miner. Spec. Pub. 33,p. 76-96. Sandberg, C. A., and Sando, U. J., 1980, Mississippian shelf margin and carbonate platform from Montana to Nevada: Fouch, 1. D., and Magathan, S. R. (eds.), Paleozoic paleogeography of the west-central United States, Rocky Mountain Paleogeography Symposium 1, Soc. Econ. Paleo. Miner., Rocky Mtn. Sect., Denver, Cob., p. 111-128. Hadley, H. D., 1950, The Charles problem: Billings Geol. Soc. Guide. 1st Ann. Fid. Conf.,p. 44-46. , 1960, Geology of the northern part of the Gravelly Range, Madison County, Montana: Billings Geol. Soc. Guide. 11th Ann. Fid. Conf., p. 149-153. Sando, U. J., and Dutro, 1. S., Jr., 1980, Geology of the Varney and Cameron quadrangles, Madison County, Montana: U. S. Gaol. Survey Bull. 1459, lOBp. Hammer, A. 4., and Lloyd, 4. M., 1926, Noteson the Quadrant Formation of east-central Montana: Amer. Assoc. Petrol. Geol. Bull., V.10,p. 986-996. Harris, U. L.1972, Upper Mississippian and Pennsylvanian sediments of central Montana: unpub. Ph.D thesis, Univ. of Montana, Missoula, 252 p. Heckel, P. H., 1972, Recognition of ancientshallow marine environments: jjRigby, S. K., and Hamblin, U. K. (eds.), Recognition of ancient sedimentaryenvironments, Soc. Econ. Pa].eo. Miner. Spec. Pub. 18,p. 226-286. 1974, Carbonate buildups in the geologic record: a review: j Laporte, L. F.(ed.), Reefs in time and space, Soc. Econ. Paleo. Miner. Spec. Pub. 18, p. 90-154. Hildreth, 6. D., 1980, The bedrock geology and stratigraphyof the Mississippian and Early Pennsylvanian rocks of the southeast flank, Armstead ant icline, Beaverhead County, Montana: unpub. MS. thesis, Oregon St. Univ., 144p. 1981, Stratigraphy of the Mississippian Big Snowy Formation of the Armstead ant icline, Beaverhead County, Montana: Mont. Geol. Soc., 1981 Fld. Conf. Southwest Montana, p. 49-57. Honkala, F. S., 1949, Geology of the Centennial region,Beaverhead County, Montana: unpub. Ph.D thesis, Univ. of Michigan, Ann Arbor, 145 p. Howard, S. D., and Reineck, H. E., 1972, Physical andbiogenic sedimentary structures of the nearshore shelf:Senckenbergia Maritima, band 4,p. 81-123. Hubbard, S. A. E. B., 1972, Stromatolitic fabric:a petrographic model: Proc. 24th I.6. C., Montreal, 7, p. 380-396. Huh, 0. K., 1967, The Mississippian systemacross the Wasatch line, east-central Idaho, extreme southwestern Montana: Mont. Gaol. Soc., 18th Ann. Fid. Conf.,p. 31-62. Iddings, J. P., and Weed, W. H., 1899, Descriptivegeology of the Gallatin Mountains: Geology of the Yellowstone National Park, U. S. Gaol. Survey Mon. 32, Pt. 2, p. 1-59. Irwin, M. L., 196!, General theory of epeiric clearwater sedimentation: Amer. Assoc. Petrol. Gaol. Bull., V. 49, p. 445-459. Isaacson, P. E.,1985, Carboniferous tectonic and eustatic carbonate cycles, foreland and platform, central Idaho: Geol. Soc. Amer. Abstracts with Programs, Rocky Mountain Sect., Boise, Idaho, p. 225. Jensen, F. S., and Carlson, K. P., 1972, TheTyler Formation in the subsurface, central Montana: Rocky Mtrt. Assoc. Geol., Geologic atlas of the Rocky Mountain region, p. 128-129. Kay, Marshall, 1951, North American qeosynclines: Geol. Soc. Amer. Mem. 48, 143p. Keenrnon, K. A., 1950, The geology of the Blacktail-Snowcrest region, Beaverhead County, Montana: unpub. Ph.D thesis, Univ. Michigafl, Ann Arbor, 207p. Kendall, A. C., 1977, Origin of dolomitemottling in Ordovician lirnestones from Saskatchewan and Manitoba: Bull. Can. Petrol. Geol., V. 25,p. 480-504. 281 Klepper, 1. R., 1950, A geologic reconnaissance of parts of Beaverhead and Madison Counties, Montana: U. S. Geol. Survey Bull. 969-C, p. 55-85. Weeks, R. A., and Ruppel, E. T.,1957, Geology of the southern Elkhorn Mountains, Jefferson and Broadwater Counties, Montana: U.S. Geol. Survey Prof. Paper 292, 82 p. Kulik, D. M., 1985, Structural and tectonic significance ofgravity interpretations and modeling in the overlap province of southwestern Montana and east-central Idaho: Geol. Soc. Amer. Abstracts with Programs, Rocky Mountain Section, Boise, Idaho,p. 250. Kupsch, W. 0., 1950, Geology of the Lima Peaksarea, Beaverhead County, Montana, and Clark County, Idaho: unpub. Ph.D thesis, Michigan Univ., 251 p. Lageson, S. R., Maughan, E. K., and Smndo, U. J.., 1975, The Mississippian and Pennsylvanian (Carboniferous) systems in the United States--Wyoming: U. S. Geol. Survey Prof. Paper 1110-U, p. U1-U38. Land, L. S., 1982, Doloraitization: Amer. Assoc. Petrol. Geol., Educ. Course Note Series 24, 20p. Laporte, L. F., 1971, Paleozoic carbonate facies of thecentral Appalachian shelf: Jour. Sed. Pet., V. 41,p. 724-740. Lucia, F. J., 1972, Recognition of evaporite-carbonateshoreline sedimentary sedimentation: j Rigby, J. K., and Hamblin, U. K.Cede.), Recognition of ancient sedimentary environments, Soc. Econ. Paleo. Miner. Spec. Pub. 18,p. 160-191. Mallory, U. U., 1967, Pennsylvanian and associatedrocks in Wyoming: U. S. Geol. Survey Prof. Paper 554-G, 31p. Mamet, B. L., Skipp, Betty, Sando, W.J., and Mapel, W.3.,1971, Biostratigraphy of Upper Mississippian and associated Carboniferous rocks in south-central Idaho: Amer. Assoc. Petrol. Geol. Bull..,V. 55,p. 2033. Mann, J. A., 1950, Geology of part ofthe Gravelly Range area, Montana: unpub. Ph.D thesis, Princeton Univ., 123p. Matti, 3. C., and McKee, E. H., 1977,Silurian and Lower Devonian paleogeography of the outer continental shelf of the Cordilleran miogeocline, central Nevada: in Stewart, 3. H., Stevens, C. H., and Fritsche, A. E. Cede.), Paleozoic paleogeography of the westernUnited States; Pacific Coast Paleogeography Symposium 1, Soc. Econ. Paleo. Miner., Pacific Section, p. 181-215. 282 Maughan, E. K., 1983, Paleogeographic setting of Pennsylvanian Tyler Formation and relation to underlying Mississippian rocks in Montana and North Dakota: Amer. Assoc. Petrol. Geol. Bull., V. 68, p. 178-195. and Roberts, A. E., 1967, Big Snowy and Amsden Groups and the Mississippian-Pennsylvanian boundary in Montana: U. S. Geol. Survey Prof. Paper 554-B, 27p. McCaleb, S.A.., and Wayhan, D. A.., 1969, Geologic reservoir analysis, Mississippian Madison Formation, Elk Basin Field, Wyoming-Montana: Amer. Assoc. Petrol. Geol. Bull., V. 53, 2094-2113. McMannis, W. 5., 1955, Geology of the Bridger Range, Montana: Amer. Assoc. Petrol. Geol. Bull. V. 66,p. 1385-1430. Miller, M. F., and Knox, L. W., 1985, Biogenic structures and deposit ional environments of a Lower Pennsylvanian coal-bearing sequence, northern Cumberland plateau, Tennessee, U. S. A.: Soc. Econ. Miner. Paleo. Spec. Pub. 35,p. 67-97. Moore, R. C., Lalicker,C. B., and Fisher,A. 5., 1952, Invertebrate fossils: McGraw-Hill, New York, 766p. Mundt, P. A., 1959, Héath-Amsden strata in central Montana: Amer. Assoc. Petrol. Geol. Bull., V. 40, p. 1915-1934. Nordquist, S. W., 1953, Mississippian stratigraphy of northern Montana: Billings Geol. Soc. Guidebook, 4th Ann. Fid. Conf., p. 68-82. Dpdyke, N. D., and Runcorn, S. K., 1959, Wind direction in the western United States in the late Paleozoic: Amer. Assoc. Petrol. Geol. Bull., V. 71,p. 959-972. Park, Robert, 1976, A note on the significance of laminations in stromatolites: Sedimentology, V. 23,p. 379-393. Peale, A. C., 1893, The Paleozojc section in the vicinity of Three Forks, Montana: U.S. Geol. Survey Bull. 110, 56p. Pecora, W. C., 1981, Bedrock geology of the Blacktail Mountains, southwestern Montana: unpub. M.S. thesis, Wesleyan Univ., Middleton, Conn., 203p. Perry, W. S., Jr., 1983, The thrust belt in the Lima-Dell,Montana area: Mont. Beol. Soc. Guidebook, 34th Ann. Field Conf.,p. 69-78. Ryder, R. 1., and Maughan, E. K.,1981., The southern part of the southwest Montana Thrust belt:a preliminary re-evaluation of structure, thermal maturationand petroleum potential: Mont. t3eol. Soc., 1981 Fid. Conf. Southwest Montana,p. 261-273. and Sando, W. 5., 1982, Sequence of deformation of Cordilleran Thrust belt in Lima, Montana region: Powers, R. B.(ed.), Geologic studies fo the Cordilleran Thrust belt, Rocky Mtn. Assoc. Geol., V. 1, p. 137-144. Wardlaw, B. R., Bostick, N. H., and Maughan, E. K., 1983, Structure, burial history, and petroleum potential of frontal thrust belt and adjacent foreland, southwest Montana: Amer. Assoc. Petrol. Geol. Bull., V. 67,p. 725743. Peterson, S. A., 1977, Paleozoic shelf-margins and marginalbasins, western Rocky Mountains-Great Basin, United States: Wyo. Geol. Assoc. Guidebook, 29th Ann. Fld. Conf.,p. 135-153. 1981, General stratigraphy and regional paleostructure of the western Montana Dverthrust belt: Mont. Geol. Soc. Guidebook, 1981 Field Conference,p. 5-35. Pevear, D. R., 1966, The esturine formation of United States Atlantic coastal plain phosphorite: Econ. Geol, V. 61, p. 251-256. Powers, M. C., 1953, A new roundness scale for sedimentary particles: Jour. Sed. Pet., V. 23,p. 117-119. Purser, B. H., and Seibold, E., 1973, The principleenvironmental factors influencing Holocene sedimentation and diagenesisin the Persian Gulf: j Purser, B.H. (ed), The Persian Gulf: Holocene carbonate sedimentation and diagenesis ina shallow epicontinental sea; New York, Springer-Verlag,p. 1-9. Rose, P. R.,1.976, Mississippain carbonate shelf margins, western United States: U. S. Geol. Survey Jour. Res., V. 4,p. 449-466. Reeves, Frank, 1931, Geology of the Big SnowyMountains, Montana: U.S. Geol. Survey Prof. Paper 165-B,p. 135-151. Reineck, H.-E., 1972, Tidal flats: j Rigby, S. K., and Hamblin, W. K.(eds.), Recognition of ancient sedimentary environments, Soc. Econ.'liner. Paleo. Spec. Pub. 35,p. 67-97. and Singh,I. B., 1980, Depositional sedimentary environments: Springer-Verlag, New York, 549p. Roberts, A. E, 1966, Insoluble residuesand Ca:Mg ratios in the Madison Group, Livingston, Montana: U.S. Geol. Survey Prof. Paper 424-B,p. B294-B296. 284 1979, Northern Rocky Mountains and adjacent plains region: Paleotectonic investigations of the Mississippian system in the United States, U. S. Geol. Survey Prof. Paper 11ø, Pt. 1, p. 221-247. Sandberg, C. A., Sutschick, R. C., Johnson, 3. 6., Poole,F. 6., and Sando, U. J., 1983, Middle Devonian to Late Mississippian geologic history of the Qverthrust belt region, western United States: Rocky Mtn. Assoc. Geol., Geologic studies of the Cordilleran thrust belt, V. 2, p. 691-719. Sando, U. 3., 1968, A new member of the MadisonLimestone (Mississippian) in Wyoming: Geol. Soc. Amer. Bull., V. 59, p. 1855-1858. ______, 1972, Madison Group (Mississippian) and Arasden Formation (Mississippian and Pennsylvanian) in the Beartooth Mountains, northern Wyoming and southern Montana: Mont. Geol. Soc. Guidebook, 21st Ann. Field Conf.,p. 57-63. 1974a, Ancient solution phenomena in the Madison Limestone (Mississippian) of north-central Wyoming: U. S. Geol. Survey Jour. Res., V. 2,p. 133-141. ______, 1974b, Bull Ridge Member of the Mission Canyon Limestone (Mississippian) of north-central Wyoming: U. S. Geol. Survey Bull. 1394-A,p. A82-A83. 1975, Mississippian (Lower Carboniferous) coral faunas of the western conterminous United States: inSokolov, B. S.(ed.), Drevnie Cnidaria Ancient Cnidaria, Novosibirsk, Nauka Pubi. House, V. 2,p. 78-83. 1976, flississippain history of the northern Rocky mountain region: U. S. Geol. Survey Jour. Res., V.4, p. 317-338. ______, 1980a, The paleoecology of Mississippian corals in the western conterminous United States: Acta Palaeontologica Polonica, v. 25,p. 619-631. 1980b, The Mississippian time scale and rock accumulation rates in the northern Rocky Mountains: Congres Internat. Stratigraphie Geologie Carbonifere, 8th, Moscow 1975 Compte Rendu, V. 6,p. 61-70. and Bamber, E. U., 1979, Coral Zonation of the Mississippian system of western North America: Neuvierne Congres International de Stratigraphie et de Geologiedu Carbonifere, V. 2,p. 289-300. 285 Gordon, Mackenzie, Jr., and Dutro, T. J., Jr., 1975, Stratigraphy and geologic history of the Amsden Formation (Mississippian and Pennsylvanian) of Wyoming: U. S. Seol. Survey Prof. Paper e48-A,p. fl1-A81. , Sandberg, C. A., and Perry, W. J., 1985, Revision of Mississippian stratigraphy, northern Tendoy Mountains, southwest Montana: U. S. Geol. Survey Bull. 1656, p. Al-AlO. Scheedlo, M. K., 1984, Structural geology of the northernSnowcrest Range, Beaverhead and Madison Counties, Montana: unpub. tl.S. thesis, Western Michigan Univ., 132p. Scott, H. W., 193!, Some Carboniferous stratigraphy inMontana and northern Wyoming: Geol. Soc. Amer. Bull., V. 43, p. 1011-1032. , 1945a, Age of the Amsden Formation: Geol. Soc. Amer. Bull., V. 56, p. 1195. 1945b, Pennsylvanian stratigraphy in Montana and northern Wyoming: Gaol. Soc. Amer. Bull., V. 56, P. 1196. Seager, 0. A., 1942, Teston Cedar Creek anticline, southeastern Montana: Amer. Assoc. Petrol. Geol. Bull., V. 26,p. 861-864. Severson, J. L., 1952, A comparison of the Madison Group (Mississippian) with its subsurface equivalents in central Montana: unpub Ph.D. thesis, Wisconsin Univ. Shaw, A. 8., 1964, Time in stratigraphy: McGraw-Hill, New York, 353 p. Shinn, E. A., 1983, Tidal flat environment: jScholle, P. A., Bebout, D. G., and Cook, C. H.(eds.), Carbonate depositional environments, Amer. Assoc. Petrol. Geol. Memoir 33, p. 171-210. , and Lloyd, R. M., 1969, Anatomy ofa modern tidal flat, Andros Island, Bahamas: Jour. Sed. Pet., V. 39, p. 1202-1228. Skipp, Betty, Sando, W. 3., and Hall,W. E., 1979, The Mississippian and Pennsylvanian (Carboniferous) systemsin the United States--Idaho: U. S. Geol. Survey Prof. Paper 1110-AP, p. AP1-PP42. Sloss, L. L., 1952, Introduction to theMississippian of the Williston basin: Billings Geol. Soc. Guidebook, Third Ann. Field Conf., p. 65-69. and Moritz, C. A.,1951, Paleozoic stratigraphy of southwestern Montana: Pmer. Assoc. Petrol. Geol. Bull., V. 35, p. 2135-2169. Smith, D. L., and Silmour, E. H, 1979, The Mississippian and Pennsylvanian (Carboniferous) systems in the United States--Montana: U. S. Geol. Survey Prof. Paper 1110-X.1 32 p. Stamm, R. 8., 1984, Conodont biostratigraphy ofthe Scott Peak Formation (Upper Mississippian) of south-central Idaho: Geol. Soc. Amer. Abstracts with Programs, Rocky Mtn.Sect., Boise, Idaho, p. 198. Stokes, W. L., 1976, What is the Wasatch Line?: In Hill, S.8. (ed.), Geology of the Cordilleran hingeline, Rocky Mtn. Assoc.Geol., 1976 Symposium Guidebook, p. 11-25. Swetland, P. 5., Clayton, S. L., and Sable, E. 13., 1978, Petroleum source-bed potential of Mississippian- Pennsylvanian rocks in parts of Montana, Idaho, Utah,and Colorado: The Mountain Geologist, Rocky Mtn. Assoc. Geol., v.14, p. 79-87. Tissot, . p., and Welte, D. H., 1978, Petroleum formation and occurrence: New York, Springer-Verlag, 538p. Tysdal, R. 6., 1970, Geology of the north endof the Ruby Range, southwestern Montana: unpub. Ph.D thesis, Univ. of Montana, 187p. Wardlaw, B. R., and Pecora, W. C., 1985, NewMississippian- Pennsylvanian stratigraphic units in southwest Montana and adjacent Idaho: LI. S. Geol. Survey Bull. 1656, Chpt. B, p. B1-B9. Weed, W. H., 1896, Yellowstone National Park;sedimentary rocks: Li. S. Geol. Survey Atlas, Folio 30. 1900, Geology of the Little Belt Mountains, Montana: U. S. Geol. Survey 20th Ann. Rpt., 1898-99,pt. 3,p. 257-451. Weimer, R. 5., Howard, S D., and Lindsay, D. R.,1981, Tidal flats and associated tidal channels:jScholle, P. A., and Spearing, Darwin (eds.), Sandstone deposit ional environments, Amer. Assoc. Petrol. Geol. Memoir 31,p. 191-245. Wentworth, C. K., 1922, A scale of gradeand class terms for clastic sediments: Jour. Geol., V. 30,p. 377-392. Williams, Howel, Turner, F. 5., and Gilbert,C. 11., 1982, Petrography: W. H. Freeman and Co., San Francisco, 626p. Wilson, S. L., 1975, Carbonate faciesin geologic history: Springer-Verlag, New York, 471p. Willis, R. P., 1959, Upper Mississippian-LowerPennsylvanian stratigraphy of central Montana and Williston Basin (North Dakota): Amer. Assøc. Petrol. Geol. Bull., v.43,p. 1940-1966. Witkind, I. J., 1964, Preliminary geologicmap of the Teepee Creek quadrangle, Montana-Wyoming: U. S. Seol. Survey, Misc. Geol. Invest. Map 1-417. 1976, Geologic map of the southern part of the Upper Red Rock Lake quadrangle, southwestern Montana: U. S. Geol. Survey, Misc. Invest. Series Map 1-943. Wunderlich, Friedrich, 1972, Beach dynamics and Beach development: Senekenbergiana rnaritima, band 4,p. 47-79. Ziegler, J.ii., 1954, Geology of the Blacktailarea, Beaverhead County, Montana: unpub. Ph.D thesis, Harvard Univ., 147p. %PPEND ICES APPENDIX A: MEASURED SECTIONS The bed thickness, splitting habit, and bedding- lamination terminology incorporated in the following measured sections is from Collinson and Thompson (1982), which represents modifications of earlier terminology of Campbell (1967) and Reineck and Singh (1973). This terminology is illustrated on the following page (fig. 60). Additional modification includes the description of bed contacts and splitting habit as planar, slightly undulatory ((1/8" total relief), and undulatory (>1/8" total relief), to supplant the term "wavy", used by Collinson and Thompson (1982). All color descriptions of fresh rock surfaces are of moistened surfaces. The petroliferous odor of the rock, described as absent, very weak, weak, moderate, strong, and very strong, refers to the odor upon striking a fresh surface with a hammer. Coral and brachiopod identifications were made by Bill Sando and Tom Dutro, Jr., respectively, of the U. S. Geological Survey. led thickness Slittin/parting Ii.b*t wtthiø beds Lanin.tton thickness I Uery thick 3e I 361 Ih,cM I I Blocky i21 I 12' lisdiun S1.bby -# I I / Thick 1/4' Is I I Nsdita' Thin 1/8 I r1.,. 1 Thin * I jS ------1 1/IS lIary thin .i..t.d thin P1*LI. . planar, diScOntinUOUs. plr, discontinuous. parallel planar, non-parellel planar, parallel non-parallel Iiiundulatory, di scanta neon., undulatory. discontinuous, parallel undulatory, nen-par.11al undulatory, parallel nan-psr.1 1*1 Fig. 60. Terminology for thickness of beds and laminations, for splitting and parting habit of units within beds, and for bedding-lamination terminology (modified from Collinson and Thompson, 1982). 290 I. RED ROCK RIVER SECTION SW 1/4, NW 1/4, section 28, 1. 13 S.,R. 7 U., Henry Gulch Quadrangle, U.S.G.S. 7.5 minute series. Lombard Limestone section measured from west to east, beginning at uppermost Mission Canyon Limestone exposure, approximately 2,640 feet west-northwest of knob in the center of section 28. The lowermost covered interval probably includes uppermost Mission Canyon Limestone, Kibbey Sandstone, and lowermost Lombard Limestone. This covered interval is characteristic throughout the southernmost end of the Snowcrest Range. To reach this location, travel due east out of Lima on the road to Lima reservoir. The road turns due north at approximately 4.8 miles from Lima, then turns east-southeast at 6.2 miles (by a gravel pit). Travel an additional 1.4 miles east to a dirt road which runs north onto a grassy bench slightly higher in elevation than the gravel road. The knob is located approximately 0.6 road miles up this dirt road, on the east side of the road. Exposure quality is poor to fair. Silty limestone intervals are characteristically very poorly exposed or covered, but the near-vertical attitude of the beds limits contamination by float from adjacent beds, permitting relatively accurate measurement and litholoqical identification (by trenching). The stratigraphically lowest exposure of the Lombard Limestone is located in the gully, immediately east of the dirt road, where it changes from a north-south to a northeast-southwest trend. 291 Unit litholopy ft. 113 COVER: Sandy soil, grayish orange (10 YR 7/4) to yellowish orange (10 YR 7/6); scattered sandstone float of same color as soil; probably basal Amsden sandstone; transition with subjacent silty limestone soil occurs overafivefootinterval...... unm. 112 COVER: Silty ,nudstone float and soil, medium gray (N5) ...... 42t5 111 BRYDZON PRCKSTONE: Olive gray (5 V 4/1), weathers to medium gray (N5); finely crystalline, trepostomous and fenestrate bryozoans, disart iculated brachiopods, echinoid ossicles and partial stems, trilobite fragments, ostracodes, small corals (SiDhonophYllia sp.), gastropods; fossils randomly distributed, most parallel bedding; weak petroliferous odor; moderately fractured, subdued rib-former...... 2 110 COVER: Graysoil, Siltymudstonechips...... 3 109 BRYOZON-BRRCHIOPOD PACKSTONE: Olive gray (5 V 4/1), weathers to medium light gray (N6); finely crystalline, crudely bedded; thick to very thick beds withmany randomly spaced, irregular fractures; trepostomous and fenestrate bryozoans, disarticulated brachiopods, echinoid ossicles and partial stems, gastropods, trilobite fragments; fossils randomly distributed, most parallel crude bedding; weak to absent petroliferous odor; rib-former...... 16 108 COVER: Gray soil with silty mudstone chips; grassy ...... 3.5 107 SPARSELY FOSSILIFEROUS WPCKESTONE: Medium olive gray (5 V 5/1), weathers to moderate yellowish brown (10 YR 5/4); microcrystalline; flaggy; echinoid and bryozoan fragments, disart iculated brachiopods; fossils randomly oriented and distributed; strong petroliferous odor...... 1 106 COVER: Gray soil with few mudstone chips...... 6 105 MUDSIONE: Dark gray (N3), weathers to medium gray (N5); microcrystalline; slightly 292 104 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray (5 Y 4/1), weathers to pale grayish orange (10 YR 8/4); microcrystalline; echinoid fragments, gastropods, disart iculated and whole pelecypods; fossils randomly oriented and distributed; many vertical fractures; moderate petroliferous odor...... 2 103SILTY MUDSTONE: Dark gray (N3), weathers to medium gray (N5); microcrystalline; sharp upper and lower contacts; poorly exposed ...... 3 102SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to pale grayish orange (10 YR 8/4); microcrystalline; no discernable bedding; echinoid fragments, disarticulated pelecypods(?); fossils randomly oriented and distributed; abundant vertical fractures; weak petroliferous odor; very subdued rib-former...... 2 101 COVER: Pale orangish gray (10 YR 8/4) to light gray (Ni) soil; scattered mudstone chips ...... 6 100SPARSELY FOSSILIFEROUS WACKESTONE: Medium olive gray (5 V 5/1), weathers to moderate yellowish brown (10 YR 5/4); flaggy; microcrystalline; echinoid and bryozoan fragments, gastropods, disarticulated and whole pelecypods; fossils randomly oriented and distributed; abundant vertical fractures; weak petroliferous odor; sharp contact with unit 99...... 1.5 99 MUDSTONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; slightly silty; very poorly exposed; strong petroliferous odor ...... 3 98 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to moderate yellowish brown (10 YR 5/4); microcrystalline; flaggy; no discernable bedding; echinoid and bryozoan fragments, whole and disarticulated pelecypods, disarticulated brachiopods('), gastropods; fossils randomly oriented and distributed; horizontal burows(?); many vertical fractures; moderate petrol i ferous odor; very subdued rib-former; sharp planarcontactwithunit99...... 2 293 97 COVER: Gray soil; grassy; few silty mudstone ch i PS...... 3 96 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to light gray (N7); microcrystalline; parallel, slightly undulatory, laminated to flaggy splitting habit; disart iculated brachiopods, echinoid debris, ostracodes, gastropods; fossils randomly oriented and distributed; extensively fractured; moderate petroliferous odor; few chert nodules; rib-former; sharp, slightly undulatory contact with unit 96...... 2 95 MUDSTDNE: Dark gray (N3); weathers to light olive gray (5 V Lit); microcrystalline; very poorly exposed ...... 1.5 94 COVER: Graysoil; grassy...... I.5 93 MtJDSTONE: Dark gray (N3), weathers to medium gray (N5); microcrystalline; very poorly exposed; sharp, planar to slightly undulatory contact with unit 92...... 1 92 BRACHIOPOD WACKESTONE: Olive gray (5 V 4/1), weathers to light olive gray (5 V 4/1) to very pale orange (1 YR 8/2); microcrystalline; very thick bed with minor parallel, undulatory, slabby to locally flaggy splitting habit; whole and disart iculated brachiopods (Product ids, Chonetes sp.?), bryozoan and echinoid debris; fossils raridomly oriented and distributed; brachiopods stand with slight relief on weathered surface; many siliceous stringers; strong fetid odor; pronounced rib-former; sharp, planar to slightly undulatory upper and lower contacts...... 5 91 NIUDSTONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; slightly silty;verypoorlyexposed...... 2 9 FOSSILIFEROUS WACKESTONE: Brownish gray (5 YR 411), weathers to medium olive gray (5 V 5/1); microcrystalline; flaggy; random, small sparry calcite patches; abundant bryozoan fragments, disarticulated and broken brachiopods, echinoid ossicles and fragments; fossils randomly oriented and distributed; extensively fractured; few small chert pods; very strong petroliferous 294 odor; pronounced rib-former; sharp, slightly undulatory upper and lower contacts ...... 1 89 MUDSTONE: Dark gray (N3), weathers to light gray (Ni) to pale grayish orange (10 YR 8/4); microcrystalline; slightly silty; poorly exposed, largely soil-covered...... 2.5 88 FOSSILIFEROUS WCKESTONE: Brownish gray (5 YR 4/1), weathers to medium light gray (N6); microcrystalline; irregular, flaggy splitting habit; abundant ramose and few fenestrate bryozoan fragments, disarticulated and broken brachiopods, echinoid ossicles, gastropods; fossils randomly oriented and distributed; few chert stringers; very strong petroliferous odor; pronounced rib-former; sharp, planar to slightly undulatory contact...... 4 87 CDVER:Graysoil;siltymudstonefloat...... 3.5 86 FDSSILIFEROLJS WACKESTONE: Medium dark gray (N4), weathers to light gray (N7); microcrystalline; flaggy; fossil hash of broken brachiopods, echinoids, bryozoans, pelecypods(?), ostracodes; fossils randomly oriented and distributed; strong petroliferous odor...... I 85 COVER: Graysoil; si].tymudstone float...... 3 84 FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to medium brownish gray (5 YR 5/1); microcrystalline; crudely bedded; echinoid ossicles and fragments, brachiopods, bryozoans, ostracodes; also corals (Sihonophvllia excentrica (Meek), and SiphonoDhyllia sp.), gastropods; fossils randomly oriented and distributed; burrows(?); moderate petroliferous odor; subdued rib-former; sharpcontactwithunit83...... 2.5 83 MUOSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; undulatory, laminated to flaggy splitting habit; no discernable bedding; slightly to moderately silty; strong fetid odor; poorly exposed...... 3.5 82 FOSSILIFEROUS WACKESTONE: Medium dark gray (N4), weathers to medium light gray (N6); microcrystalline; irregular, flaggy splitting habit; disarticulated and 295 broken brachiopods (including Weospirifer raenuntius Easton), pelecypods(?), and echinoids; also corals (Siohonophyllia sp.), ramose bryozoan debris, ostracodes; fossils randomly oriented and distributed; bioturbated; strong petroliferous odor; subdued rib-former; sharp, planar contact with unit 83...... 3 81 COVER: Graysoil; silty mudstone float...... 4 80 SPPRSELY FOSSILIFEROUS WACKESTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; small disart iculated brachiopods, ostracodes, echinoid debris; fossils randomly oriented and distributed; burrows; moderate petroliferous odor; very subdued rib-former; sharp, undulatory contact with unit 79...... 1 79 FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to light gray (Ni); microcrystalline; no discernable bedding; undulatory, non-parallel, laminated to flaggy splitting habit; slightly silty; small, disarticulated brachiopods, echinoid ossicles, indeterminate fossil fragments; fossils parallel bedding, randomly distributed; very strong petroliferous odor; moderately well exposed; sharp, undulatory upper and lower contacts...... 2 78 SPARSELY FOSSILIFEROUS WACKESTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; echinoid debris, small disarticulated brachiopods, ostracodes(?); fossils randomly distributed,most parallel bedding; moderate petrol iferous odor; subdued rib-former; sharp, undulatory upper and lower contacts...... 2 77 FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; no discernable bedding; undulatory, non-parallel, laminated to flaggy splitting habit; slightly silty; small, disarticulated brachiopods, echinoid debris, ostracodes; fossils randomly distributed, most parallel bedding ; strong petroliferous odor; moderately well exposed; sharp, undulatory to slightly undulatory upper and lower contacts...... 4 296 76 SPARSELY FOSSILIFEROUS WACKESTONE: Dark gray (N3), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; flaggy; small disarticulated brachiopods (including Productids), echinoid debris, ostracodes; fossils randomly distributed, most subparallel to bedding; horizontal burrows; moderate petroliferous odor; subdued rib-former; sharp, slightly undulatory contact with unit 77...... 2 7 COVER: Gray soil; silty mudstone float ...... 8 74 SPARSELY FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; undulatory, non-parallel, laminated to flaggy splitting habit; slightly silty; few ostracodes, disarticulated brachiopods, echinoid debris; fossils randomly distributed, parallel bedding; strong petroliferous odor; poorly exposed; sharp, slightly undulatory contact with unit 73...... 1 73 SPARSELY FOSSILIFEROUS WACKESTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; flaggy to slabby; small, disarticulated brachiopods, echinoid ossicles and partial stems, ostracodes, indeterminate mollusk fragments; fossils randomly distributed, most subparallel bedding; moderate petroliferous odor; subduedrib-former...... 3 72 COVER: Gray soil; grassy; silty mudstone float...... 71 SPARSELY FOSSILIFEROUS WACKESTONE: Dark gray (N3), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; echinoid fragments, small disarticulated brachiopods and pelecypods(?); fossils randomly distributed, most parallel bedding; moderate petroliferous odor; subdued rib-former; sharp, planar to slightly undulatory contact with unit 70...... 1 70 SPARSELY FOSSILIFEROUS MUDSIONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; undulatory, non-parallel, laminated to flaggy splitting habit; ostracodes(?), echinoid fragments, small disarticulated brachiopods; fossils randomly distributed, parallel bedding; moderate petroliferous odor; poorly exposed; sharp, 297 slightly undulatory upper and lower otats . 2 69 FOSSILIFEROUS WACKESTONE: Dark gray (N3), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; slabby; disarticulated brachiopods (including Ovatia cf. 0. muralis Gordon, Limipecten cf. otterensis Easton) and pelecypods(?), ostracodes, echinoid ossicles and fragments, indeterminate orthoconic nautiloid mold; most fossils parallel bedding, randomly distributed; burrows; strong fetid odor; subtle rib-former; sharp, slightly undulatory upper and lower contacts...... 3 68 SPARSELY FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; undulatory, non-parallel, laminated to flaggy splitting habit; many dark gray wisps on weathered surface; few small, disart iculated brachiopods, ostracodes, echinoid fragments; fossils randomly distributed, most parallel bedding; horizontal burrows; strong petrol iferous odor; sharp, slightly to moderately undulatory upper and lowercontacts...... 2 67 SPARSELY FOSSILIFEROUS WACKESIONE: Dark gray (N3), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; flaggy to slabby; small, disarticulated brachiopods and pelecypods(?), echinoid ossicles and fragments, ostracodes(?); fossils randomly distributed, most parallel bedding; strong fetid odor; subdued rib-former; sharp, moderately undulatory contact with unit 68...... 2 66 COVER: Graysoil; grassy...... 7 65 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; undulatory, parallel, laminated to flaggy splitting habit; disarticulated and broken brachiopods, echinoid ossicles; fossils randomly oriented arid distributed; moderate petrol iferous odor; subdued rib-former; sharp, slightly undulatory contact with unit 64...... 1 64 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to yellowish gray (5 V 8/1); microcrystalline; slabby; disarticulated and broken brachiopods, echinoid ossicles and few partial sterns; fossils randomly oriented and distributed; moderate petroliferous odor; subdued rib-former...... 2 63 COVER: Gray to grayish orange (10 YR 714> soil; abundant mudstone and silty mudstone chips...... 8 62 FOSSILIFEROUS MUDSIONE: Medium gray (N5), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; undulatory, non-parallel to parallel, laminated to flaggy splitting habit; few disarticulated brachiopods, echinoid ossicles; fossils randomly oriented and distributed; strong petroliferous odor; subdued rib-former...... 1 61 COVER: Gray soil; silty mudstone and fossiliferous mudstone chips...... 3 60 FOSSILIFEROUS MUDSTONE: Medium gray (N5), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; undulatory, non-parallel to parallel, flaggy splitting habit; echinoid ossicles, disarticulated brachiopods, ostracodes (?); fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; subdued rib-former...... 2 59 COVER: Gray to grayish orange (10 YR 7/4) soil, moderately grassy; abundant silty mudstone and fossiliferous mudstone chips...... 27 58 FOSSILIFEROUS MUDSTONE: Meduium dark gray (NA), weathers to light olivegray (5 Y 6/1); microcrystalline; undulatory, parallel, laminated to flaggy splitting habit; disarticulated and broken brachiopods, echinoid ossicles; fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; subdued rib-former; sharp, slightly undulatory contact with unit 57...... 2 57 FOSSILIFEROUS MUDSTONE: Medium dark gray (N5), weathers to yellowish gray (5 '1 8/1); microcrystalline; disarticulated brachiopods, echinoid ossicles and partial sterns; fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; subdued rib-former...... I 299 56 COVER: Gray soil; silty mudstone chips. 9 35 FOSSILIFEROUS MUOSTONE: Medium dark gray (N4), weathers to light olive gray (3 V 6/1); microcrystalline; undulatory, parallel, laminated to flaggy splitting habit; few disarticulated brachiopods, echinoid ossicles, indeterminate fossil fragments; fossils randomly distributed, subparallel to bedding; strong petroliferous odor; subdued rib-former...... 2 54 COVER: Grayish orange (10 YR 7/4) soil; silty mudstorie and fossiliferous mudstone chips; grassy...... 17 53 FOSSILIFEROUS MUDSTONE: Medium gray INS), weathers to light gray (N7); microcrystalline; slabby; echinoid ossicles and partial stems, disarticulated brachiopods; fossils randomly oriented and distributed; moderate petroliferous odor; subdued rib-former; sharp, slightly undulatorycontact with unit 52...... 1 32 FOSSILIFEROUS MUDSTONE: Medium gray INS), weathers to light gray (N7); microcrystalline; no discernable bedding; undulatory, non-parallel to parallel, laminated to flaggy splitting habit; small disarticulated brachiopods, echirioid ossicles, indeterminate fossil debris; fossils subparallel bedding, randomly distributed; moderate petroliferous odor; subdued rib-former; sharp, slightly undulatory contact with overlying unit 53, but gradational intounit5l...... 3 51 FOSSILIFEROUS MUDSTONE: Medium gray INS), weathers to light gray (N7); microcrystalline; thick bed; slabby; disarticulated brachiopods and pelecypods(?), echinoid ossicles and fragments; fossils subparallel to bedding, randomly distributed; moderate petrol iferous odor; sharp, slightly undulatory contact with unit 50...... 2 50 FOSSILIFEROUS MUDSIONE: Medium dark gray (N4), weathers to medium light gray (N6); microcrystalline; undulatory, parallel, laminated to flaggy splitting habit; few disarticulated brachiopods, echinoid ossicles; fossils randomly oriented and 300 distributed; strong petroliferous odor; subdued rib-former . 1 49 COVER: Gray to grayish orange (10 YR 7/4) soil; siltyrtiudstonechips...... 48 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to pale yellowish brown 10 YR 6/2); microcrystalline; disarticulated and broken brachiopods and pelecypods(?), echinoid ossicles; fossils randomly oriented and distributed; moderate petroliferous odor; subdued rib-former...... 1 47 COVER: Grayish orange (10 YR 7/4) soil; fossiliferous(?) mudetone and silty mudstone chips...... 6 46 FOSSILIFEROUS MUOSTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; undulatory, non-parallel to parallel, laminated to flaggy splitting habit; disarticulated brachiopods, echinoid ossicles and partial stems, ostracodes(?); fossils randomly oriented and distributed; moderate petroliferous odor; subdued rib-former...... 2 4 COVER: Grayish orange (10 YR 7/4) soil; fossiliferous and silty mudstone chips...... a 44 FOSSILIFEROUS MUOSTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; no discernable bedding; undulatory, parallel, laminated to flaggy splitting habit; disarticulated brachiopods and pelecypods(?), echinoid ossicles and fragments; fossils randomly oriented and distributed; moderate petroliferous odor; subdued rib-former; sharp, slightly undulatory contact with unit 43...... 3 43 FOSSILIFEROUS MUOSTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; slabby; disarticulated brachiopods, echinoid ossicles and partial stems, ostracodes; fossils randomly oriented and distributed; moderate petroliferous odor; subdued rib-former; sharp slightly undulatory upper and lower contacts...... 1. 42 FOSSILIFEROUS MUOSTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; undulatory, non-parallel to 301 parallel, laminated to flaggy splitting habit; disarticulated brachiopods, echinoid ossicles, ostracodes; fossi is randomly oriented and distributed; strong petroliferous odor; subdued rib-former...... 2 41 COVER: Grayish orange (10 YR 7/4) soil; silty mudstone and fossiliferous mudstone chips; grassy...... 12 40 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; undulatory, parallel, laminated to flaggy splitting habit; disarticulated and broken brachiopods and pelecypods(?), echinoid ossicles and partial stems, ostracodes; fossils randomly oriented and distributed; strong petroliferous odor; subdued rib-former...... 2 39 COVER: Grayish orange (10 YR 7/4) soil; grassy; silty mudstone and fossiliferous mudstone chips; low-relief saddle...... 89 38 FOSSILIFEROUS PACKSTDNE: Medium dark gray (N4), weathers to medium gray (N!); microcrystalline; minor parallel, planar to slightly undulatory, slabby splitting habit; disarticulated brachiopods, echinoid ossicles, bryozoan fragments, gastropods; fossils randomly distributed, most subparallel to bedding, many broken; moderate petroliferous odor; subdued rib-former; sharp, slightly undulatory to locally planar contact with unit 37...... 2 37 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to medium light gray (N6); microcrystalline; undulatory, non-parallel laminated to flaggy splitting habit; no discernable bedding; locally disturbed, thin to medium lamina; echinoid ossicles, few disarticulated brachiopods; fossils randomly distributed, most subparallel to bedding; strong petroliferous odor; moderately well exposed...... 2 36 FOSSILIFEROUS PACKSTONE: Medium dark gray (N4), weathers to medium gray (N!); microcrystalline; slabby; many echinoid ossicles, few partial stems, disarticulated brachiopods, gastropods ("),brycszoan fragments; fossils randomly oriented and distributed; moderate petroliferous odor; 302 subdued rib-former; sharp, slightly undulatory upper and lower contacts...... I 35 COVER: Gray soil; fossiliferous mudstone chips...... 4 34 FOSSILIFEROUS MUDSTONE: Methum dark gray (N4), weathers to light gray(N7); microcrystalline; non-parallel, undulatory, flaggy splitting habit; locally disturbed to slightly deformed (flame structures?), thin to medium lamina; echinoid ossicles, disart iculated brachiopods, gastropods, ostracodes; fossils subparallel to bedding, randomly distributed; moderate petrol iferous odor; subdued rib-former...... 1 33 COVER: Gray soil; fossiliferous mudstone and silty rnudstone chips...... a. . . 7 32 FOSSILIFEROUS PPCKSTONE: Medium dark gray (N4),weathers to medium gray(N5); microcrystalline; flaggy to slabby; echinoid ossicles and partial stems, disarticulated brachiopods, fenestrate and ramose bryozoan fragments, gastropods, foranunifera; fossils randomly oriented and distributed; moderate petroliferous odor; moderately well pronounced rib-former...... 2 31 COVER: Grayish orange(10 YR 7/4)to gray soil; fossiliferous mudstone and silty mudetone chips...... 3 30 FOSSILIFEROUS PCKSTONE:Medium dark gray (N4),weathers to light gray (N7); microcrystalline; echinoid ossicles, disart iculated brachiopods, ostracodes, gastropods; fossils randomly oriented distributed; moderate petroliferous odor; very subdued rib-former...... 0.5 29 COVER: Grayish orange (10 YR7/4) soil; silty mudstone and fossiliferous rnudstone chips...... 10.5 28 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to medium lightgray (N6); microcrystalline; parallel to locally non-parallel, undulatory, laminated to flaggy splitting habit; faint, thin to medium lamiria visible on weathered surface; few echinaid ossiclas, small disart iculated brachiopods, ostracodes; 303 fossils subparallel to bedding, locally concentrated into discrete layers, but randomly distributed in upper part of unit; moderately petroliferous odor; subdued rib-former; sharp, slightly undulatory contact with unit 29...... 2 27 FOSSILIFEROUS PACKSTONE: Medium gray (N4), weathers to medium gray (N5); microcrystalline; medium-bedded; planar; echinoid ossicles and partial stems; disart iculated brach iopods, ostracodes, and pelecypods(?), gastropods, trilobites, fenestrate and ramose bryozoan debris; fossils randomly oriented and distributed, many broken; moderate petroliferous odor; moderately well pronounced rib-former; sharp, slightly undulatoryupper and lower contacts. aa a a . . s a a a . . a a a a a a a a a a a a ...... 3 26 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to lightgray (N7); microcrystalline; no discernable bedding; parallel, undulatory, laminated to flaggy splitting habit; faint, thin to medium lamina on weathered surface; few echinoid ossicles, small disarticulated brachiopods; fossils subparallel to bedding, randomly distributed; strong petroliferous odor; subdued rib-former; sharp, slightly undulatory upper and lower contacts; poorly tomoderatelywellexposed...... S 25 FOSSILIFEROUS PCKSTONE:Medium dark gray (N4), weathers to medium lightgray (N6); microcrystalline; echinoid ossicles, disart iculated brachiopods, bryozoan debris, pelecypodr?) fragments, foraminifera; fossils randomly oriented and distributed; moderate petroliferous odor; subdued rib-former...... 1 24 COVER: Gray to grayish orange (10 YR 7/4) soil; silty rnudstone and fossiliferous mudstone chips; grassy...... 6 23 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; undulatory non-parallel to parallel, slightly undulatory to undulatory, laminated to predominantly flaggy splitting habit; few echinoid ossicles, disarticulated brachiopods; fossils subparai.lel to 304 bedding, randomly distributed; moderate petroliferous odor; very subdued rib-former...... 2 22 ECHINOID PPCSTONE: Medium dark gray (N4), weathers to yellowish gray (5 V 8/1) to very pale orange (10 YR 8/2); microcrystalline; planar, siabby splitting habit; many echinoid ossicles and plates, few partial stems, disarticulated brachiopods and pelecypods, ostracodes, forarninifera, bryozoan debris; fossils subparallel to bedding, concentrated into very thin, discrete layers separated by extremely thin mud laminae; strong petroliferous odor; moderately well pronounced rib-former; sharp, slightly undulatory to locally planar upper and lower contacts...... 2 21 FOSSILIFEROUS MUDSTDNE: Medium dark gray (N4), weathers to pale yellowish brown (10 YR 6/2); microcrystalline; parallel to non-parallel, undulatory, laminated to flaggy splitting habit; echinoid ossicles, disarticulated brachiopods; fossils subparallel to bedding, randomly distributed; moderate to strong petroliferous odor; very subdued rib-former; moderately well exposed; sharp, slightly undulatory upper and lower contacts...... 3 20 FOSSILIFEROUS PCKSTONE:Medium dark gray (N4), weathers to light brownishgray (5 YR 6/1); finely crystalline (slightly recrystallized); parallel, planar, slabby splitting habit; echinoid plates and ossicles, few partial stems, disarticulated brachiopods, ostracodes, bryozoan debris; fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; subdued rib-former; sharp, slightly undulatory contact with unit 21...... 4 19 COVER: Grayish orange (10 YR 7/4) soil; silty mudstone and fossiliferous rnudstone chips...... 9 18 FOSSILIFEROUS PPCKSTONE: Medium dark gray (N4), weathers to yellowishgray (5 V 8/1); microcrystalline; parallel, planar to slighty undulatory, slabby splitting habit; echinoid ossicles and plates, disarticulated brachiopods and pelecypods(?), gastropods; fossils subparallel to bedding;moderate 305 petroliferous odor; subdued rib-former; sharp, slightly undulatory lower contact with unit 17...... 3 17 FOSSILIFEROUS MUDSTONE: Medium dark gray (M), weathers to light gray (N7); microcrystalline; non-parallel to predominantly parallel, undulatory, laminated to flaggy splitting habit; few echinoid ossicles, disarticulated brachiopods; fossils subparallel to bedding; strong petroliferous odor; very subdued rib-former; sharp, planar to locally slightly undulatory contact with unit 16...... 1 16 FOSSILIFEROUS PACKSTONE: Medium dark gray (N4), weathers to yellowishgray (5 Y 8/1); microcrystalline; flaggy to slabby; echinoid ossicles, partial stems, disarticulated brachiopods and pelecypods C?), ostracodes, gastropods, bryozoan(?) debris; fosi is subparallel to bedding, randomly distributed; moderate petroliferous odor; subdued rib-former...... 2 15 COVER Grassy slope; trenching indicates dark gray CN3); non-fossiliferous to sparsely fossiliferous mudstone...... 96 14 FOSSILIFEROUS MUDSTQNE: Very pale yellowish brown (10 YR 7/2), weathers to lightgray (N7); microcrystalline; thick bed; random, irregular horizontal fractures; echinoid ossicles, disarticulated brachiopods, gastropods; fossils randomly oriented and distributed; horizontal burrows; strong fetid odor; subdued rib-former...... 2 13 SPARSELY FOSSILIFEROUS WACKESTONE: Medium dark gray (N4), weathers to yellowish gray (5 V 8/1); microcrystalline; thick bed; few vertical fractures; few echinoid ossicles and partial stems, small disarticulated and broken brachiopods, ostracodes; fossils randomly oriented and distributed; many dark carbonaceous(?) wisps subparallel to bedding; burrows('1); moderate petroliferous odor; silty mudstone partings separate underlying and overlying units; sharp, slightly undulatoryupper arid lower contacts...... 3 306 12 FOSSILIFEROUS MUDSIONE: Medium dark gray (N4), weathers to pale grayish orange (10 YR 8/4); microcrystalline; non-parallel, planar to slightly undulatory, flaggy splitting habit; echinoid ossicles and fragments, d isart iculatecl brachiopods, ostracodes, indeterminate grazing(?) trailson splitting planes; fossils randomly oriented and distributed; moderate petroliferous odor; sharp, planar contact withuriderlyingunitil...... 1 11. SILTY FOSSILIFEROUS MUDSTONE:Brownish gray (5 YR 4/1), weathers to light olivegray (5 Y 6/1); microcrystalline; abundant quartzose silt; non-parallel, planar flaggy to predominantly laminated splittinghabit; ostracodes, few echinoid ossicles and brachiopod fragments; most fossils parallel to bedding, randomly distributed, rarely locally clustered; horizontalburrows; gradational transition with underlying unit 10...... 2 10 FOSSILIFEROUS-PELLETAL MUDSTCNE:Dark olive gray (5 V 3/1), weathers to liht olive gray (5 V 611); microcrystalline; parallel, planar to slightly undulatory, flaggy splitting habit; ostracodes, echinoid ossicles and fragments, gastropods;abundant pellets; most fossils parallel to bedding, randomly distributed; horizontalburrows(?); very subdued rib-former...... 5 9 COVER: Light brownish gray (5 YR 6/1) soil; silty mudstone and fossiliferous niudetone chips...... 20 8 FOSSILIFEROUS MLJDSTONE: Olive black (5 V 2/1), weathers to very lightgray (N8); microcrystalline; medium beds with parallel to non-parallel, planar, flaggysplitting habit; silty mudstone partingsbetween beds; faint parallel, very thin laminaelocally; whole and disarticulated brachiopodsand pelecypods, echinoid ossicles, gastropods; fossils subparallel to bedding; fewblack (carbonaceous?) wisps; few small, grayish orange (10 YR 7/4), augen-shaped chert nodules; very subdued rib-former;sharp, planar to slightly undulatory 7...... 3 307 7 SPARSELY FOSSILIFEROUS WCKESTONE: Olive gray (5 V 4/li, weathers to yellowishgray (5 V 7/2); microcrystalline; parallel, planar to slightly undulatory, flaggy splitting habit; echinoid ossicles, few partial stems, few whole pelecypods, ostracodes; fossils randomly oriented and distributed, stand with moderate relief on weathered surface; horizontal and subhorizontal burrows; strong petrol iferous odor; subdued rib-former; sharp, slightly undulatorycontactwithunit6...... 3 6 FOSSILIFEROUS MUDSTONE: Black (Ni), weathers to very light gray (N8); microcrystalline; medium beds with parallel, planar to slightly undulatory, flaggy to slabby splitting habit, several thin fissile intervals (1-2 inches thick); faint, very thin, parallel laminations locally visible on weathered surface; ostracodes, few echinoid ossicles, few disarticulated pelecypods; fossils parallel bedding, randomly distributed; few grayishorange (10 YR 7/4) augen-shaped chert nodules; few black, carbonaceous(?) wisps subparallel to bedding; very strong petroliferous odor; very subdued rib-former; sharp, slightly undulatory contact with unit S...... S CALCREDUS SHALE: Black (Ni), weathers to light gray (N7); microcrystalline; silty; parallel, planar, fissile to laminated splitting habit; very thin, parallel larainae; non-fossiliferous(?); very strong petroliferous odor; moderately well exposed; sharp, slightly undulatory contact with unit 4...... 2 4 FOSSILIFEROUS NUDSIONE: Srayish black (N2), weathers to very light gray (N8); microcrystalline; thin to medium beds with parallel, slightly undulatory to planar, fissile to laminated splitting habit, alternating with medium beds witha parallel, slightly undulatory to planar, flaggy to blocky splitting habit; fissile to laminated interbeds progressively decrease in thickness upsect ion; few echinoid ossicles and fragments, ostracodes, disarticulated pelecypods; fossils parallel to bedding, randomly distributed; few YR 7/4), augen-shaped chert nodules; very subdued rib-former; sharp, slightly undulatory contact with unit 3...... 24 3 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to yellowish gray (5 V 8/1); microcrystalline; thin to medium beds with parallel, slightly undulatory, fissile to laminated splitting habit alternating with medium beds with parallel, planar to slightly undulatory, flaggy to blocky splitting habit; very thin, parallel laminae locally visible on weathered surface; alternating bed types subequal in number; few echinoid ossicles and fragments, whole and disarticulated brachiopods and pelecypods, few gastropods; most fossils subparallel to bedding, randomly distributed, stand with slight relief on weathered surface; many black, carbonaceous(?) wisps, many large (up to 8 inches long), grayish orange (10 YR 7/4), augen-shaped chert nodules; moderate to strong petroliferous odor; very subdued rib-former; sharp, slightly undulatory contact with unit 2...... 7 2 FOSSILIFEROUS MUDSTONE: Olive gray (5 V 4/1), weathers to light gray (N7); microcrystalline; thin to medium beds with parallel, planar to moderately undulatory, fissile to laminated to locally flaggy splitting habit, alternating with medium beds with parallel, planar to slightly undulatory, flaggy to blocky splitting habit; fissile to laminated interbeds progressively decrease in thickness in upper third of unit; disarticulated ostracodes and pelecypods, echinoid and gastropod fragments; fossils parallel bedding, randomly distributed; rare, small, grayish orange (10 YR 7/4), augen-shaped chert nodules; very subdued rib-former...... 19 COVERS gray to grayish orange (10 YR 7/4) soil; narrow zone of admixed grayishorange (10 YR 7/4) to moderate yellowish brown (10 YR 3/4) soil in lower 110 20 feet; silty, non-fosslilferous, arid fossiliferous mudstone chips; grassy; this interval is covered throughout the southwestern end of the range...... (229 TOTflL: 894.0 feet 309 II. CLOVER DIVIDE SECTION NW 1/4, SE 1/4, and SE 1/4, NW 1/4, section23, 1. 12 S.,R. 6 W., Whiskey Spring quadrangle, U.S.G.S.7.5 minute series. Lombard Limestone section measured alongnorth-northwest to south-southeast traverseon hillside on the east side of the road along the west fork of Blacktail DeerCreek, beginning approximately 2.7 miles south of the confluencewith Moonshine Gulch. The lower 1,032 feet of the Lombard,characterized by black, non-fossiliferous to fossiliferousraudstone, is probably fault thickened. Two southwest-northeast-trending stream valleys dissect the lower part of theLombard and parallel the major north-down normal fault approximately 1.2miles to the northwest, which juxtaposes Tertiary and LowerMississippian units. Bedding attitudes of the few poorly exposed LombardLimestone beds in the sections between these two valleysand the Mission Canyon Limestone are at high angles to thesouthwest-northeast trend of the Paleozoic units in thisarea; up to800 ofsinistral rotation is suggested by the northwest-southeaststrike of these poorly exposed beds. The strike of the beds in theupper 991 feet of the Lombard parallels the strike ofsurrounding Paleozoic units in this area. The Lombard Limestone is poorly to moderatelywell exposed at this location, on the southeast limb ofa large, northeast-trending anticline. Talus obscures many parts of this section, however exposures on the north side andthe upper part of the west side of the hillare adequate for measurement. Many thick beds crop out in this section,but most of them are less than 1.5 feet thick. The Kibbey Sandstone is missing here. The fault-thickened lower part of the Lombard,which is juxtaposed against the brecciated liniestones of theupper part of the Mission Canyon Limestone, and thepresence of the Kibbey at the Sawtooth Mountain area, only 4.4 milesto the northeast, both suggest that the Kibbey has been locallyfaulted out. The amount of fault thickening in the lowerpart of the Lombard is uncertain, but a minimum of 880 feet of extrasection may be present, based on a comparison with therelatively complete, 1,143 foot thick section at SawtoothMountain. Zeigler (1954) measured 1,783 feet of Lombard Limestone here,but Perry (1983) has calculated a tectonicallyenhanced thickness of 2,350 feet. The amount of missing section inthe uppermost Mission Canyon Limestone here also isunknown. Corals in the uppermost exposed Mission Canyon beds are ofearly Meramecian age (Coral Zone III), suggesting thata minimum amount of section is missing; some of the thinning may be attributed to subaerialerosion related to regression of the Madisonsea in Meramecian time, although faulting associated with thedevelopment of the Snowcrest Range must also beconsidered. No corals were found in this section,however brachiopods are common and are often well preserved. Two species of brachiopods were retrieved from thefloat at the base of the hills one identical and twodifferent species were found in the 310 described beds and/or float at discrete stratigraphic levels. The two species found at the base of the hill. are Composita cf. subcivadrata (Hall) and nthracospirifer curvilateralis (Easton). The three species found in the upper part of the Lombard are Rnthracospirifer curvilaterplis (Easton), Antiguatonia sp., and Composita sp. The occurrence of these brachiopods, common to the late Paleozoic, and the stratigraphic position of these dark, fossiliferous and non-fossiliferous limestones between lithologies characteristic of the Mission Canyon Limestone and Arnsden Formation support the assignment of these rocks to the Lombard Limestone. This location can be approached from either the north or south, although the approach from the north is the shortest and easiest route to drive. To approach from thenorth, drive approximately 37 miles south from Dillon along the Blacktail Deer Creek road. From the south, drive east from Lima to Lima Reservoir dam. Continue approximately 8.7 miles east, staying north of the reservoir, until the road turn abruptly north. Follow the road north to the 1-junction with Blacktail Deer Creek Road. Turn northwest and continue approximately 7.3 miles to the hillside exposure. 311 Unit Litholopy Ft. 63 COVER: Very pale orange (10 YR 8/2) to pale grayish orange (10 YR 8/4) soil; scattered sandstone float, grayish orange (10 YR 7/4) to moderate reddish brown (10 R 4/6); basal msden Formation; small, massive sandstone outcrop 10' above inferred Lombard-msden contact ...... unm. 62 COVER: Medium brownish gray (5 YR 5/1) soil; abundant fossiliferous packstone and wackestone float, containing echinoid ossicles, disarticulated brachiopods, ostracodes, bryozoan fragments, high-spired gastropods; also non-fossiliferous mudstone float; several large wackestone/packstone float blocks (up to 5' diameter); relatively abrupt change in soil color at top (inferred contact); uppermost Lombard Limestone ...... 185 61 FOSSILIFEROUS PRCKSTONE: Dark olive gray (5 V 3/1), weathers to very light gray (N7); microcrystalline; thick beds with minor, discontinuous, parallel, slightly undulatory to undulatory, slabby splitting habit, alternating with thin to medium beds with non-parallel to parallel, undulatory, flaggy splitting habit; sharp, slightly undulatory to undulatory contacts between beds; vertical fractures ubiquitous in thick beds; echinoid ossicles, indeterminate ramose bryozoan fragments, disarticulated and broken brachiopods, tightly coiled gastropods; fossils randomly oriented and distributed; burrows(); moderate petrol iferous odor; ledge-former; well-exposed...... 9 60 COVER: Non-fossiliferous mudstone float, fossiliferous wackestone and packstone float ...... 7 59 FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to yellowish gray (5 V 8/1); microcrystalline; medium to thick beds with minor parallel, slightly undulatory to undulatory, flaggy to slabby splitting habit, alternating with thin to medium beds with parallel to non-parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; 312 echinoid ossicles, disarticulated and broken brach i opods, fenestrat e and indeterminate bryozoan fragments, ostracodes; fossils randomly oriented and distributed; moderate petrol iferous odor; subdued ledge-former; poorlytomoderatelywellexposed...... 14 58 COVER: Fossiliferous wackestone and mudstone float ...... 8 57 BRCHIOPOD WACKESTONE/PCKSTONE: Olive gray (5 V 4/1), weathers to medium gray (N5); microcrystalline; medium to thick beds with minor parallel, planar to slightly undulatory, flaggy to slabby splitting habit, alternating with thin to medium beds with parallel to non-parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; many disarticulated and few whole brachiopods (including Composita sp.), echinoid ossicles, Cochliodont fish teeth, ostracodes; many fossils subparallel to bedding (weak shape fabric), randomly distributed; fossils more concentrated in few thin intervals (=packstones) within wackestone beds; weak petroliferous odor; subdued ledge-former; moderately well exposed; sharp, planar to slightly undulatorycontactwithunit56...... 6 56 FOSSILIFEROUS WCKESTONE: Brownish black (5 YR 2/1), weathers to medium light gray (N6); microcrystalline; medium beds with parallel, slightly undulatory, flaggy splitting habit, alternating with thin beds with parallel, undulatory, laminated splitting habit; sharp, slightly undulatory to undulatory contacts between beds; whole and disarticulated brachiopods (chiefly Productids and Spiriferids), echinoid ossicles, indeterminate bryozoan(?) fragments; ostracodas; fossils randomly oriented and distributed; strong petroliferous odor; ledge-former...... 4 55 COVER: Fossiliferous wackestone float, fossils in float include Pntiguatonia sp. and nthracospirifer curvilateralis Easton...... 6 54 FOSSILIFEROUS WACI minor parallel, slightly undulatory, flaggy splitting habit, alternating with thin to medium beds with parallel, slightly undulatory to undulatory, laminated to locally fissilo splitting habit; sharp, slightly undulatory to undulatory contacts between beds; many disarticulated and few whole brachiopods (also few broken), indeterminate bryozoan fragments, ostracodes, gastropods; fossils subparal lel to bedding to randomly oriented, randomly distributed; few whole brachiopods with geopetal fill; moderate to strong petroliferous odor; many thin, intermittent covered intervals; scattered ledge outcrops...... 12 53 COVER: Fossiliferous wackestone and mudstone float; indeterminate trilobite mold in float ...... 6 52 FOSSILIFEROUS WACKESTONE: Brownish black (5 V 2/1), weathers to light gray (N7); microcrystalline; medium beds with very minor parallel, slightly undulatory, flaggy splitting habit, alternating with thin to predominantly medium beds with parallel to non-parallel, slightly undulatory to undulatory, laminated to locally fissile splitting habit; echinoid ossicles, few whole and many disarticulated brachiopods, ostracodes(?); fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; subdued ledge-former...... 9 51 COVER: Fossiliferous wackestone and mudstone float...... 4 50 FOSSILIFEROUS WACKESTONE: Dark brownish gray (5 YR 3/1), weathers to medium light gray (N6); microcrystalline; medium beds (thinner than unit 52 beds) with ubiquitous vertical fractures and very minor, parallel, slightly undulatory, flaggy splitting habit, alternating with medium beds with parallel to non-parallel, undulatory, fissile to laminated splitting habit; echinoid ossicles, disart iculated brachiopods, gastropods; fossils subparallel to bedding, randomly distributed; strong petroliferous odor; subdued ledge-former...... 3 49 COVER: Fossiliferous wackestone and rnudstone float...... 3 314 48 FOSSILIFEROUS PCKSTONE: Olive gray (5 V 4/1), weathers to light gray (N6); microcrystalline; medium to thick beds with minor parallel, planar to slightly undulatory, flaggy to slabby splitting habit, alternating with medium beds with parallel, slightly undulatory to undulatory, laminated to locally fissile splitting habit; few small, irregular to ovoid, olive black (5 V 2/1) mud lenses; echinoid ossicles, whole and disarticulated brachiopods, disarticulated pelecypods and trilobites, indeterminate bryozoan fragments, ostracodes; fossils subparallel to bedding, randomly distributed, stand with slight relief on weathered surface; weak petrol iferous odor; ledge-former...... 4 47 COVER: Fossiliferous packstone and wackestone float, minor fossiliferous mudstone float...... 6 46 FOSSILIFEROUS PPCKSTONE: Medium olive gray (5 V 5/1), weathers to medium gray (N5); microcrystalline; medium to thick beds (few thin beds) with parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with medium (few thick) beds with parallel, slightly undulatory to undulatory, laminated to locally fissi].e splitting habit; sharp, slightly undulatory to undulatory contacts between beds; many disarticulated and few whole pelecypods, disart iculated brachiopods, abundant broken valves, echinoid ossicles, few bryozoan fragments, few disarticulated trilobites, ostracodes; fossils well packed, randomly oriented and distributed, stand with slight to moderate relief on weathered surface; weak petroliferous odor; subdued ledge-former, moderately well exposed, few thincovered intervals...... 15 45 COVER: Fossiliferous wackestone and packstone float, minormudstone float...... 9 44 FOSSILIFEROUS WACKESTONE/PACKSTONE: Olive black (5 V 2/1), weathers to lightgray (N7); microcrystalline; medium beds with parallel, slightly undulatory to undulatory, flaggy splitting habit, alternating with medium beds with parallel, slightly undulatory to undulatory, laminated to locally fissile splitting habit; sharp, slightly undulatory contacts between beds; 315 echinoid ossicles and fragments, disarticulated and few broken brachiopods, disarticu].ated and few whole pelecypods, fenestrate bryozoan fragments, ostracodes; fossils randomly oriented and distributed; slight lateral variations in fossil density (local packstones); scarce, very small pyrite masses; moderate petroliferous odor; subdued ledge-former...... 4 43 COVER: Fossiliferous wackestone and mudstone float ...... S 42 FOSSILIFEROUS WCKEST0NE/PACKSTDNE: Olive black ( V 2/1), weathers to light gray (N7); microcrystalline; medium to thick beds with absent to common, parallel, slightly undulatory to undulatory, flaggy to slabby splitting habit, alternating with medium to thick beds with parallel to locally non-parallel, undulatory, fissile to predominantly laminated splitting habit; sharp, slightly undulatory contacts between beds; disarticulated and broken brachiopods, echinoid ossicles, disart iculated pelecypods, ostracodes, indeterminate bryozoan fragments; fossils randomly oriented and distributed, locally subparallel to bedding, locally concentrated/densely packed (packstones); swirled texture common (=bioturbation); moderate petrol i ferous odor; subdued ledge-former to local ledge-former; poorly exposed...... 21 41 COVER: Fossiliferous wackestone and mudstone float...... 11 40 FOSSILIFEROUS WCKESTONE: Olive black (5 V 2/1), weathers to light gray (N7); microcrystalline; medium to thick beds with minor parallel, slightly undulatory to undulatory, flaggy to slabby splitting habit, alternating with medium beds with parallel, slightly undulatory to undulatory, laminated to locally fissile splitting habit; sharp, slightly undulatory to undulatory contacts between beds; echinoid ossicles, disarticulated brachiopods and pelecypods; fossils randomly oriented and distributed; local swirled texture (bioturbation); moderate petroliferous odor; subdued ledge-former...... 9 316 39 COVER: Fossiliferous wackestone and mudstone float, minor non-fossiliferous mudstone float...... lI 38 FOSSILIFEROUS MUDSTONE: Dark brownish gray (5 YR 3/1), weathers to medium light gray (N6); microcrystalline; medium to thick beds with minor parallel, slightly undulatory, slabby splitting habit, alternating with thick beds with parallel, slightly undulatory, fissile to predominantly laminated splitting habit; sharp, slightly undulatory contacts between beds; thin, planar to slightly undulatory laniina, locally grade upward into slightly swirled texture; lamina absent locally; few echinoid ossicles, ostracodes, disarticulted brachiopods, finely comminuted fossil debris; fossils parallel to bedding, randomly distributed; few randomly oriented burrows; moderate petrol iferous odor; subdued ledge-former; laminated beds poorly exposed...... 14 37 COVER: Mudstone and fossiliferous mudstone float...... 6 36 FOSSILIFEROUS MUDSTONE: Dark brownish gray (5 YR 3/1), weathers to medium light gray (N6); microcrystalline; medium to thick beds with minor parallel, slightly undulatory, slabby splitting habit alternating with medium to thick beds with parallel, slightly undulatory to undulatory, laminated to locally fissile splitting habit; sharp, slightly undulatory contacts between beds; thin, planar to slightly undulatory lamina, pass vertically into non-laminated intervals; few echinoid ossicles, disarticulated brachiopods and pelecypods('), finely comminuted fossil. debris; fossils subparallel to bedding, randomly distributed; few augen-shaped chert nodules (up to 3" high, 7" long); moderate petroliferous odor; subdued ledge-former...... 13 35 COVER: Fossiliferous and non-fossiliferous mudstone float...... 6 34 FOSSILIFEROUS WCKESTONE: Olive black (5 V 2/1), weathers to lightgray (N7); microcrystalline; medium beds with minor 317 parallel, slightly undulatory, flaggy splitting habit, alternating with thick beds with parallel, slightly undulatory to undulatory, laminated to locally fissile splitting habit; sharp, slightly undulatory contacts between beds; thin, planar to locally slightly undulatory lamina; few echinoid ossicles, disarticulated brachiopods and pelecypocis, ostracodes(?); fossils subparallel to bedding, randomly distributed; few small burrows; few small chert nodules; moderate petroliferous odor; subdued ledge-former...... 4 33 COVER: Fossiliferous and non-fossiliferous mudstone float...... 32 FOSSILIFEROUS WACKESIDNE: Olive black (5 V 2/1), weathers to light gray (N7); microcrystalline; medium beds with parallel, planar to slightly undulatory, flaggy splitting habit, alternating with medium to thick beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory to locally planar contacts between beds; faint, planar lamina visible on weathered surface; disarticulated and broken brachiopods and pelecypods, echinoid ossicles and fragments; fossils subparallel to bedding, randomly distributed but locally concentrated in thin layers; moderate petroliferous odor; subdued ledge-former to local ledge-former...... 17 31 COVER: Fossiliferous wackestone and mudstone float...... 8 30 FOSSILIFEROUS MUOSTONE: Dark olive gray (3 V 3/1), weathers to lightgray (N7); microcrystalline; medium beds with minor parallel, slightly undulatory, flaggy splitting habit, alternating with medium to thick beds with parallel, slightly undulatory, fissile to laminated splitting habit; thin, planar to slightly undulatory lamina locally visible on weathered surface; few echinoid fragments, disarticulated brachiopods; fossils subparallel to bedding, randomly distributed; moderate to strong petroliferous odor; very subdued ledge-former; poorly exposed...... 7 318 29 COVER: Fossiliferous wackestone and mudstone float, non-fossiliferous mudstone float...... 23 28 FOSSILIFEROUS WRCKESTONE: Olive black (5 V 2/1), weathers to medium lightgray (N6); microcrystalline; thick beds with parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with medium to thick beds with parallel, slightly undulatory to undulatory, laminated to locally fissile splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles and fragments, disarticulated and few broken brachiopods and pelecypods, disart iculated trilobites, ostracodes, few fish teeth("); fossils subparallel to bedding, randomly distributed, some slightly more concentrated in thin layers; moderate petroliferous odor; subdued ledge-former...... 12 27 COVER: Fossiliferous wackestone and mudstone float...... 9 26 FOSSILIFEROUS WCKESTONE:Dark olive gray (5 V 2/1), weathers to lightgray (N7); microcrystalline; medium to thick beds with parallel, slightly undulatory to locally undulatory, flaggy to slabby splitting habit, alternating with medium to thick beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; faint, planar to slightly undulatory lamina locally visibleon weathered surface; echinoid ossicles, disart iculated and broken brachiopods, few pelecypods, few disarticulated trilobites, few broken gastropods(?); fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; ledge-former...... 7 25 COVER: Fossiliferous wackestone and rnudstone float...... 11 24 FOSSILIFEROUS MUDETONE: Dark brownish gray (5 YR 3/1),weathe-s to medium lightgray (N6); microcrystalline; medium and thick beds with minor discontinuous, parallel, slightly undulatory, flaggy to slabby splitting habit; sharp, slightly undulatory contacts between beds; faint, 319 planar to slightly undulatory lamina locally visible on weathered surface; echinoid ossicles and fragments, disarticulated and broken brachiopods, few broken pelecypods(?); fossils subparallel to locally parallel to bedding, randomly distributed; strong petrol iferous odor; subdued ledge-former...... 3 23 COVER: Fossiliferous wackestone and mudstone float, non-fossiliferous mudstone float...... 4 22 FOSSILIFEROUS MUDSTONE: Dark brownish gray (5 YR 3/1), weathers to medium lightgray (N6); microcrystalline; medium beds with minor to locally significant, parallel, planar to slightly undulatory, flaggy splitting habit, alternating with medium to predominantly thick beds with parallel, slightly undulatory to undulatory, laminated to locally fissile splitting habit; sharp, slightly undulatory to locally planar contacts between beds; thin, slightly undulatory lamina locally visible on weathered surface; echinoid ossicles and fragments, disarticulated and few broken pelecypods and brachipods, ostracodes; most fossils subparallel to bedding, randomly distributed; few short, randomly oriented burrows; moderate petroliferous odor; subdued ledge-former...... 12 21 COVER: Fossiliferous and non-fossiliferous mudstone float; minor fossiliferous wackestone float...... 16 20 SPARSELY FOSSILIFEROUS WACKESTONE: Olive black (5 Y 2/1), weathers to lightgray (N7); microcrystalline; medium and thick beds with minor discontinuous, parallel, slightly undulatory, flaggy to slabby splitting, habit, alternating with medium to thick beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, slightly undulatory to undulatory contacts between beds; echinoid ossicles,many disarticulated and very few whole brachiopods and pelecypods, ostracodes; most fossils subparallel to bedding, randomly distributed; local, vertical variations in fossil density (alternatingvery thin arid thin fossiliferous mudstone and wackestone layers); few burrows("); strong 320 petroliferous odor; subdued 1ed-forer .9 19 COVER: Fossiliferous wackestorie and mudstone float, non-fossiliferous mudstone float...... 24 18 FOSSILIFEROUS WACKESTONE/MUDSTONE: Dark olive gray (Z V 3/1), weathers to medium light gray (N6); microcrystalline; medium beds with very minor, discontinuous, parallel, slightly undulatory, flaggy splitting habit, alternating with medium to thick beds with parallel, undulatory, fissile to laminated splitting habit; sharp, slightly undulatory to undulatory contacts between beds; echinoid ossicles and fragments, disart iculated brachiopods and pelecypods, ostracodes, gastropods; fossils randomly oriented and distributed; few mudstone beds, predominantly wackestone beds; moderate to strong petroliferous odor; subdued ledge-former to local ledge-former (wackestones); laminated intervals moderately well to predominantly poorly exposed...... 13 17 COVER: Fossiliferous wackestone and mudstone float, non-fossiliferous mudstone float...... 8 16 SPARSELY FOSSILIFEROUS WACKESTONE: Olive black (5 V 2/1), weathers to lightgray (N7); microcrystalline; medium to thick beds with parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with thick beds with parallel, slightly undulatory to undulatory, fissile to predominantly laminated splittinghabit; sharp, slightly undulatory to locally undulatory contacts between beds; echinoid ossicles, whole and disarticulated pelecypods and (few) brachiopods, high-spired gastropods, ostracodes; fossils randomly oriented and distributed, fossils less concentrated locally (=thin mudstone intervals); moderate petroliferous odor; ledge-former...... 5 15 COVER: Fossiliferous and non-fossiliferous mudstone float; minor fossiliferous wackestone float...... 11 14 SPARSELY FOSSILIFEROUS WACRESTONE: Olive black (5 V 2/I), weathers to mediumlight gray (Ne); microcrystalline; medium beds with discontinuous, parallel,slightly 321 undulatory, flaggy splitting habit, alternating with medium to thick beds with parallel, slightly undulatory to undulatory, fissile to predominantly laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, disart Iculated pelecypods and brachiopods, ostracodes; fossils randomly oriented and distributed; strong petroliferous odor; subdued ledge-former; separated from unit 13 by medium/laminated bed, with sharp, slightly undulatory contact. . *...... 13 FOSSILIFEROUS MUDSTDNE: Dark olive gray (5 V 3/1), weathers to lightgray (N7); microcrystalline; medium beds with parallel, slightly undulatory, flaggy splitting habit, alternating with medium to thick beds with parallel, undulatory, laminated tolocally fissile splitting habit; sharp, slightly undulatory to locally planar contacts between beds; echinoid ossicles and fragments, ost racades, few gast ropods, few disarticulated pelecypods(?);fossils randomly oriented and distributed; horizontal burrows; strong petrol iferous odor; subdued ledge-former...... a ...... 7 12 COVER: Fossiliferous and non-fossiliferous cnudstone float...... 3 11 SPARSELY FOSSILIFEROUS WC}(ESTONE: Olive black (5 V 2/1), weathers to mediumlight gray (N6); microcrystalline; thick bed with minor, discontinuous, parallel, slightly undulatory, flaggy splitting habit, between two very poorly exposed beds with parallel, undulatory,laminated splitting habit; echinoid ossicles and fragments, disarticulated and broken pelecypods and brachiopods, high-spired gastropods; fossils randomly orientedand distributed; moderate petroliferousodor; ledge-former...... 2 10 COVER: Fossiliferous and non-fossiliferous mucistone float...... 4 9 FOSSILIFEROUS N1UDSTONE: Dark olive gray (5 'f 3/1), weathers tovery pale orange (10 YR 8/2) to lightgray (N7); microcrystalline; thick beds with minor 322 discontinuous, parallel, planar to slightly undulatory, flaggy to slabby splitting habit, alternating with thick beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, few gastropods, few disarticulated pelecypods; fossils randomly oriented and distributed; strong petroliferous odor; subdued ledge-former...... 6 8 COVER: Fossiliferous and non-fossiliferous rnudstone float...... 3 7 FOSSILIFEROUS MUDSTONE: Dark olive gray (5 V 3/1), weathers to lightgray (N7); microcrystalline; thick bed with parallel, planar to slightly undulatory, flaggy to slabby splitting habit, between two poorly exposed beds with parallel, slightly undulatory to undulatory, laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, disarticulated pelecypods, ostracodes, few gastropods; fossils randomly oriented and distributed; strong petroliferous odor; subdued ledge-former...... 2 6 COVER: Vegetated; scattered fossiliferous and non-fossiliferous mudstone float; dark brownish gray soil...... 295 5 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to lightgray (N7); microcrystalline; thick(?) beds with parallel, planar to slightly undulatory, fissile to predominantly laminated splitting habit; echinoid ossicles, whole and disart iculated pelecypods, ostracodes, few gastropods; fossils parallel to bedding, randomly distributed; strong petroliferous odor; subdued ledge-former...... 3 4 COVER: Grassy; dark brownishgray soil; fossiliferous and non-fossiliferous niudstone float...... 4 3 FOSSILIFEROUS MUDSTONE/WC}cESTONE: Olive black (5 V 2/1) to black (Ni),weathers to light gray (N7) to very paleorange (10 YR 8/2); microcrystalline;medium to predominantly thick beds with absentto 323 minor, parallel, planar to slightly undulatory, slabby to blocky splitting habit, alternating with thick tovery thick beds wtih parallel, planar to slightly undulatory, fissile to laminated splitting habit; variable contacts between beds: some sharp and planar to slightly undulatory, most gradational contacts;many slabby/blocky beds grade laterally into fissile/laminated beds; faint,very thin to thin, planar lamina locally visibleon weathered surface; whole and disarticulated pelecypods (few with geopetal fill), few disart iculated brachiopods, ostracodes, echinoid ossicles and few partial stems, gastropods; most fossils parallel to bedding, many concentrated in discrete layers, others randomly distributed; fossils locally in pod-shaped clusters; indeterminate (grazing C?), feeding C?)) trace fossils on many bedding planes; few beds with local, denser concentrationof fossils (=wackestones); strong petroliferous odor; ledge-former...... 38 2 COVER: Brownish black (5 YR 2/1) soil; scattered fossiliferous and non-fossiliferous mudstone float;rare, small, scattered outcrops of fossiliferous o predominantly non-fossiliferous mudst one; weakly discernable bedding striking at high anglestobedsofunits3-G3...... 1,032 BRECCITED WCKESTDNE: Dark olive gray (5 V 3/1), weathers to medium lightgray (N6); microcrystalline; thick tovery thick beds, crudely bedded, massive to locally blocky splitting habit; many disarticulated and few whole pelecypods and brachiopods (many Spiriferids), echinoid ossicles, corals (including Vesiculophyllurnsp. and Diphyphyllum ep.), few ostracodes; fossils randomly oriented and distributed, local weak shape fabric, stand with slight relief on weathered surface; moderateto strong petroliferous odor; locally brecciated, underlain by limestone solution breccias and paleokarst...... unfli. TOTPL: 2,023.0 feet 324 III. SAWTOOTH MOUNTAIN SECTION Sections 8 and 9, 1. 12 S.1R. 5 W., Antone Peak quadrangle, U.S.G.S. 7.5 minute series. Kibbey Sandstone and Lombard Limestone section measured at twolocations: units 1-5 measured on north-facing cliffs just west of the head ofIndian Creek (NW 1/4, SE 1/4, NE 1/4, section 9);units 6-60 measured at prominent hill (summit elevation 9,566')just west-northwest of the western end of Sawtooth Mountain, insection 8. Units 6-12 measured on dip slope on the south-southeastside of the hill in section 8 (NW 1/4, SE 1/4, and at SW 1/4,NE 1/4, section 8). Units 13-60 measured on the west-northwestside of the hill, at W 1/2, SW 1/4, and at SE 1/4, NE1/4, NW 1/4, section 8. The Kibbey Sandstone isvery poorly exposed in this area, but one 12-foot thick ledgesequence crops out at the edge of the talus apron at the base of the westside of the hill in section 8. Unit 18 (Lombard Limestone) is bestexposed as cliffs just north-northeast of the summit of the hillin section 8. Unit 6 (Lombard Limestone) is exposed ina large gully at the base of the dip slope of the previouslymentioned hill. Several feet of unit 6 shales also crop out atthe base of the north-facing cliffs (section 9), but the relationshipof these shales with those in the gully, with respect tothe true stratigraphic thickness of this unit, is uncertain. Based on this uncertainty, and because the shalesequence exposed in the gully is the thickest of the two exposures, thevalue obtained in the gully is used in this report; this thicknessvalue is considered a minimum value. This area can be approached from thesouth or from the northeast. To approach from the south, driveup Antone Peak Road (FR 325) to Cornell Camp (NE 1/4,section 20). Hike north along Cornell trail to Sawtooth trail,turning northeast at this junction and proceeding along thelatter trail to the west end of Sawtooth Mountain. To approach from the northeast, drive east-southeast on the East Fork BlacktailDeer Creek Road until it ends at Indian Creek (section34, 1.11 9.,R. S W.). Hike across Indian Creek and then continue south-southwestalong Sawtooth trail, paralleling thecreek most of the way to the north face of Sawtooth Mountain. Both access roads branch off of Blacktail Deer Creek Road,so approaches from both Linia and Dillon are possible. These roads traverse severalexposures of Tertiary clays and, asa result, are very slippery and unsafe to travel during and immediatelyafter heavy rains. 325 Unit Litholopy Ft. 60 UflRTZ ARENITE: Pale yellowish brown (10 YR 612), weathers to moderatebrown (5 YR 4/4) to very paleorange (10 YR 8/2); fine to medium grained; calcite-cemented; small, subangular to subrounded limestone clasts along base of unit; crudely normal graded; ledge-former...... unm. Sf3 MUDSTONE: Color mottled; moderate brown (5 YR 3/4) and very light olivegray (3 V 7/i.), weathers to moderatebrown (5 YR 4/4) and medium lightgray (N6), respectively; few small, oval to round, very light gray (N8) mottles; microcrystalline; medium, planar to undulatory bed with minor parallel, undulatory, flaggy splitting habit; vertical fractures ubiquitous;sharp, undulatory (2" relief), erosional contact with unit 60; sharp,slightly undulatory contact with unit 58; moderate petroliferous odor; subdued ledge-former...... 1 58 MUDSTCNE: Dark yellowish brown (10YR 412), weathers to light olivegray (5 V 6/1) to light gray (N7); microcrystalline;parallel, to non-parallel, undulatory,thin beds with calcareous shale partings; non-fossilifeous; non-rhythmic ripples(?) with 1/2"relief; bioturbated; few burrows(?);very small chert nodules; moderatepetroliferous odor; subdued ledge former...... 6 57 MUDSIONE: Faintly color mottled; olivegray (5 V 4/1) and light olivegray (5 V 6/1), weathers overall to pale grayishorange (10 YR 8/4) to pale brown(5 YR 5/2); microcrystalline; planar, thickbeds with minor parallel, planar toslightly undulatory, flaggy to slabbysplitting habit, alternating with medium to predominantly thin, planarbeds with parallel, planar to undulatory,fissile to laminated splitting habit;bioturbated(?); non-fossiliferous; minor dolomite associated with mottles; pyritecommon in darker mottles; color graduallychanges upsection to dark yellowishbrown (10 YR 7/2) and dark yellowishorange (10 YR 6/2) mottles, weatherto pale yellowish brown (10 YR 6/2)and pale 326 yellowish orange (10 YR 816),respectively; pyrite absent in upper part ofunit; weak petrol iferous odor; subduedledge-former; gradational contacts with units 58and 56...... 41 56 DOLOMITIC MUDSTONE: Color mottled: brownish gray (5 YR 4/1) and medium olivegray (5 Y 511), weathers to olivegray (5 V 4/1) and yellowishgray (5 V 7/2), respectively; microcrystalline; planar, medium to thick beds with parallel, planar to very slightly undulatory, laminated to flaggy splitting habit; non-fossiliferous; bioturbated(?); burrows(?); disseminatedpyrite; weak petroliferous odor; ledge-former; gradational contact with underlying shales (unit 55)...... $ ...... 19 CNOTE: section description traverse offset 0.9 miles to large gully withexcellent shale outcrops; NW 1/4, SE 1/4,section 8) 53 CALCAREDUS SHALE: Black (Ni), weathers to yellowish gray (5 V 8/1); silty; microcrystalline; thin, planar bedswith parallel, planar to very slightly undulatory, laminated to predominantly fissile splitting habit;very thin, planar lamina visibleon weathered surface; minor pyrite; very strong petroliferous odor; well exposed; slope-former...... 42 54 COVER: Grassy dip slope; fossiliferous wackestone and packstone float; minor limestone conglomerate float...... 8 53 LIMESTONE CONGLOMERATE: Pebbles and cobbles, Black (Ni) to moderate olivegray (5 V 4/2) to dark brownishgray (5 YR 3/1), set in pale yellowishorange (10 YR 8/6) to grayish orange (10 YR7/4) matrix; weathers overall to mediumgray (N5) to yellowish gray (5 V 7/2);no discernable bedding; parallel, undulatory,flaggy to slabby splitting habit; clastsof non-fossiliferous mudstone, sparsely fossiliferous and fossiliferouswackestone, phosphatic pellets; many clastswith internal iron stainas several discrete bands parallel to clast margins;matrix of "floating" fossils (disarticulatedand broken brachiopods and pelecypods,bryozoan and trilobite debris, echinoidossicles), 327 limestone granules, inicrite, sparry calcite, and quartzose silt; poorly sorted; clasts subangular to predominantly rounded, equidimensional to elongate; no shape fabric; lensoidaiC?) deposit (local occurrence, thins laterally, absent elsewhere on dip slope); moderately well exposed; very subdued ledge-former...... 3 52 COVER: Grassy dip slope; fossiliferous wackestone and packstone float (similar to float of unit 50)...... 10.5 51 FOSSILIFEROUS PcICKSTONE: Medium gray (145), weathers to grayish orange (10 YR 7/4); microcrystalline; no discernable bedding; parallel, planar to slightly undulatory, flaggy to slabby splitting habit; fenestrate bryozoan debris, whole and disarticulated brachiopods (few broken), echinoid ossicles, few gastropods; most fossils parallel to bedding, randomly distributed, stand with slight reliefon weathered surface; weak petroliferous odor; very subdued ledge-former; poorly exposed...... 1.5 50 COVER: Grassy dip slope; fossiliferous wackestone and packstone float; wackestone contains abundant bryozoan fragments, echinoid ossicles, whole and disarticulated brach iopods, ostracodes; packstonefloat similar to unit 51; also scattered, whole to slightly broken, largecup corals (including Sthhonoohvlliasp., Michelinia cf. meekana Girty) andbrachiopods (includingntiQuatonia aff. pernodosa Easton, Inflatia aff. j richardsiGirty, nthracospirifer curvilateralis Easton)...... 21 49 FOSSILIFEROUS GRAINSTONE: Brownish gray (5 YR 4/1), weathers to mediumolive gray (5 Y 5/1); microcrystalline;no discernable bedding; parallel, slightly undulatory, blocky splitting habit; echinoidossicles, disart iculated and broken brachiopods, fenestrate and indeterminateramose bryozoan fragments, few whole pelecypods, gastropods, ostracodes; most fossils parallel to bedding, randomly distributed, stand with moderate reliefon weathered surface; weak petroliferous odor;very subdued ledge-former, poorly exposed...... 2 48 COVER: Grassy; scattered grairistone float...... 4 328 47 FOSSILIFEROUS GRINSTONE: Brownish gray (5 YR 4/1), weathers tomedium olive gray (5 Y 5/1); microcrystalline;no discernable bedding; parallel, slightlyundulatory, flaggy splitting habit; echinoidossicles and fragments; fenestrateand indeterminate ramose bryozoan fragments, disarticulated and broken brachiopods,ostracodes, gastropods; most fossils parallelto bedding, randomly distributed;weak petroliferous odor; very subdued ledge-former...... 1 46 COVER: Grassy; minor fossiliferouspackstone and grainstone float...... 7 45 FOSSILIFEROUS Pc%CKSTONE: Medium brownish gray (5 YR 5/1), weathers to mediumolive gray (5 V 511); moderately saccharoidal (recrystallized); medium(?) beds with parallel, slightly undualtory,slabby splitting habit; echinoidossicles, bryozoan fragments (fenestellid, trepostome, and rhabdomesidvarieties), whole and disarticulatedbrachiopods (including Composita sp.) andpelecypods, corals (includingmplexizaphrentis sp.), gastropods, tn lobites, indeterminate orthoconic nautiloid debris; fossils randomly oriented and distributed,stand with slight reliefon weathered surface; few, small sylolites;slickensides on fracture surfaces; very weakpetroliferous odor; subdued ledge-former;poorly exposed...... 3 44 COVER: Grassy; fossiliferouswackestone and packstone float...... 12 43 FOSSILIFEROUS PC} burrows; weak to moderate petroliferous odor; ledge-former...... 15 42 COVER: Grassy; fossiliferous wackestone float...... 5 41 BRYOZON WCKESToNE/PgCKSTONE:Brownish gray (5 YR 4/1), weathers to lightgray (N7) to grayish orange (10 YR 7/4); microcrystalline; thick, planar wackestone beds with parallel to non-parallel, undulatory, flaggy splitting habit, alternating with medium, planar beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; fissile intervals pass laterally into laminated intervals; two thin, slightly undulatory packstone interbeds with parallel, undulatory, laminatedsplitting habit occur near top of wackestonebeds; fenestrate, rhabdomesid, and trepostome bryozoans (many long,ramose and dendroid fragments), disarticulated brachiopods, echinoid ossicles, gastropods; most fossils parallel to bedding, randomly distributed; packstone interbeds predominantly bryozoans, and pinch out laterally over a few tens offeet; subdued ledge-former; moderatelywell exposed...... 6 40 COVER: Grassy; scarce fossiliferous wackestone float...... 4 39 8RYOZON WCKESTONE: Brownish gray (5 YR 4/1),weathers to very light gray (N8) to pale orange (10 YR8/2); microcrystalline; thick to predominantly medium, planar beds with parallelto locally non-parallel, undulatory,flaggy splitting habit, alternatingwith thin to medium, planar beds withparallel, planar to undulatory, fissile topredominantly laminated splitting habit; fissileintervals pass laterally into laminated intervals; fenestrate, rhabdomesid, andtrepostome bryozoan fragments (many long,ramose arid dendroid fragments), disarticulated brachiopods (including Cornpositasp., many indeterminate Spiriferids andProductids), echinoid ossicles, tightly coiled gastropods, ostraccides; most fossils parallel to bedding, few at highangles, randomly distributed, stand withmoderate relief on weathered surface;few chert 330 pods and stringers (up to 18"long), primarily in thin to medium, laminated beds; moderate petroliferousodor; subdued ledge-former; laminated and fissile intervals typically poorly to moderately well exposed...... 19 38 COVER: Grassy; fossiliferous wackestorie float...... 5 37 FOSSILIFEROUSPACKSTONE: Dusky yellowish brown (10 YR 2/2), weathers topinkish gray (5 YR 8/1); microcrystalline; thick(?) beds with parallel, planarto slightly undulatory, laminated to flaggy splitting habit; whole and disarticulated brachiopods, echinoid ossicles,ramose bryozoan debris; fossils subparallelto bedding, randomly distributed;moderate petroliferous odor; very subtle ledge-former; poorly exposed...... 4 36 COVER: Grassy;fossiliferouswackestone and packstone float...... 9 35 BRCHIOPDD PCKSTONE:Medium dark gray (N4), weathers to pinkish gray (5 YR8/1); microcrystalline; thick beds with parallel, planar to slightly undulatory,flaggy to laminated splitting habit, alternatingwith thin to very thin limy shalebeds (slightly silty); disarticulated and fewbroken brachiopods, echinoid ossicles,ramose bryozoans; most fossils parallel tobedding, randomly distributed; few, localintervals slightly lessfossiliferous(=wackestones); subdued ledge-former; poorly exposed(small, scatterd exposures withmany thin, intermittent covered intervals)...... 27 34 COVER: Grassy; fossiliferous wackestone and packstone float...... 17 33 BRACHIOPOD WCKESTONE/PACKSTONE: Medium dark gray (N4), weathers to brownishgray (5 YR 4/1); microcrystalline;thick, planar beds with parallel, slightlyundulatory to undulatory, flaggy to slabby splitting habit, alternating with thin limyshale beds (slightly silty); predominantly disarticulated and few broken brachiopods, echirioid ossicles, cryptostorne(?)bryozoan fragments, ostracodes; most fossils parallel to bedding, randomlydistributed; 331 brachiopods most abundant (packstones)in flaggy intervals; local, small mud injection structures from limy shale interbeds; moderate petroliferous odor; subdued ledge-former; moderatelywell exposed, few thin covered intervals...... 36 32 COVER: Mudstone and fossiliferous wackestone float...... 13 31 FOSSILIFEROUS WPCKESTDNE/PACKSTONE: Dark gray (N3), weathers to light olivegray (5 V 6/1); microcrystalline;medium to predominantly thick beds with parallel, planar to slightly undulatory, laminatedto flaggy splitting habit, alternatingwith medium to predominantly thin,slightly undulatory limy shale beds; wholeand disarticulated brachiopods (including Anthracospirifer curvilateralis Easton), echinoid ossicles, gastropods, bryozoanand coral (?) fragments, ostracodes;fossils randomly oriented and distributed; lateral variations in fossil density create a variable wackestone topackstone lithology locally, but wackestonesmost common; crops out as small, scattered ledges with many thin, intermittent covered intervals...... 42 30 FOSSILIFEROUS MUOSTONE: Medium dark gray (N4), weathers to light olivegray (5 V S/I); microcrystalline;thick, planar to slightly undulatorybeds with parallel, planar to slightlyundulatory, slabby to blocky splittinghabit alternating with thick, slightlyundulatory beds with parallel, planarto slightly undulatory, laminated splittinghabit; slabby/blocky beds grade upwardinto slightly thicker flaggy beds,but sharp contact between flaggy and overlying slabby/blocky beds; very few echinoid ossicles, ostracodes; fossilssubparallel to bedding, randomly distributed;few burrows('); very strongpetroliferous odor; very subdued ledge-formerto slope-former; poorly exposed...... 28 29 COVER: Mudstone float...... 3 28 ECHINOID PACKSTONE: Olive gray (5 V 4/1), weathers to medium lightgray (N6); microcrystalline; thick, planarbeds with 332 parallel, planar to slightlyundulatory, flaggy splitting habit,alternating with thin to medium, slightlyundulatory, slightly silty, lirny shale beds;many echinoid ossicles (includingPentacririus) and partial stems, bryozoanfragments, disarticulated and broken brachiopods, gastropods; fossils randomlyoriented and distributed; moderate petroliferous odor; very subdued ledge-former...... 4 27 COVER: Mudstone and fossiliferouspackstone float ...... 0.4 25 ECHINOID PCKSTONE: Olive gray (5 V 4/1), weathers to medium gray (N5); microcrystalline; thick, planarbeds with parallel, planar to slightlyundulatory, flaggy to rarely slabby splittinghabit, alternating with thin to mediumbeds with parallel, slightly undulatory,fissile to laminated splitting habit;fissile intervals slightly siltier;many echinoid ossicles (including Pentacrinus)and partial stems, disarticulatedand broken brachiopods, bryozoan fragments,gastropods; fossils randomly oriented and distributed; moderate petroliferousodor; subdued ledge-former...... 15 25 COVER: Silty limestone and fossiliferous wackestone float...... 11 24 FOSSILIFEROUS WCKESTONE: Pale brown (5 YR 5/2), weathers tovery light gray (Na); microcrystalline;thick to very thick, planar beds withparallel, planar to slightly undulatory,flaggy to less commonly slabby or blocky splittinghabit, alternating with thin to mediumbeds with parallel, undulatory,discontinuous to continuous, fissile to laminatedsplitting habit; bryozoan fragments,echinoid ossicles, whole and disarticulated brachiopods, disarticulatedpelecypods(?); fossils randomly orientedand distributed; moderate petroliferous odor;subdued ledge-former; laminated/fissileintervals typically poorly exposed tocovered...... 24 23 COVER: Silty shale and fossiliferous wackestone float...... 6 333 22 FOSSILIFEROUS WCKESTONE: Olive gray (5 V 4/1), weathers to mediumlight gray (N6); microcrystalline; mediumto thick (rare very thick beds), planarbeds with parallel, planar to slightly undulatory, flaggy splitting habit, alternatingwith thin to medium beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit;fissile intervals slightly silty; echinoid ossicles and partial stems, whole anddisarticulated brachiopods (including Spirifer cf. brazerianus Girty), few small and broken corals(?), ostracodes; fossils randomly oriented and distributed;one 5" thick storm(?) layer of concentratedfossil debris (fossils parallel to bedding) approximately 3' above base of unit; few vertical to inclined burrows; fewsmall chert stringers; moderatepetroliferous odor; subdued ledge-former; laminated/f issile intervals variably exposed, typically poorly exposed...... 21 21 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to lightgray (N7); microcrystalline; thick, planar beds with parallel, planar to slightly undulatory, flaggy splitting habit, alternatingwith thin beds with parallel, slightly undulatory, laminated to predominantly fissile splitting habit; thin,fissile beds display crude thickeningupward trend; sharp, slightly undulatoryto undulatory contacts between beds;very few brachiopod fragments;fossil; subparallel to bedding, randomly distributed; very strong petroliferous odor; subdued ledge-former; sharp, undulatorycontact with unit 22...... S 20 COVER: Mudstone and fossiliferous mudstone float...... 17 19 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to lightgray (N7); microcrystalline; medium to thick,planar beds with parallel, planarto slightly undulatory, flaggy splittinghabit, alternating with thin beds oflimy shale; few brachiopod fragments;fossils parallel to bedding, randomlydistributed; very strong petrolifarous odor;subdued ledge-former...... 10 334 18 COVER: Mudstone float... . 4 17 MUDSTONE: Dark gray (N3), weathers to light gray (Ni); microcrystalline; medium,planar beds with parallel, planar toslightly undulatory, flaggy splittinghabit, alternating with thin beds oflimy shale; very thin, planar lamina locally visible on weathered surface; non-fossil iferous(?); very strong petroliferous odor; poorly exposed ...... * ...... 6 16 COVER: Mudstone float...... 11 15 FOSSILIFEROUS MLJDSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; medium, planar bedswith parallel, slightly undulatory,flaggy splitting habit, alternatingwith thin beds of limy shale;very thin, planar lamina visible on weathered surface;few brachiopod(?) fragments obliqueto lamina, randomly distributed;very strong petroliferous odor;very subdued ledge-former ...... 16 14 COVER: Mudstone and fossiliferousmudstone float...... 7 13 FOSSILIFEROUS MUDSTONE: Medium dark 'gray (N4), weathers tovery light gray (N8); microcrystalline; slightly silty;bedding poorly exposed, butgenerally thin to medium with parallel, slightlyundulatory, f].aggy splitting habit,alternating with thin beds of limy shale;few echinoid ossicles, ostracodes(?); fossilsrandomly oriented and distributed,stand with slight relief on weatheredsurface; very strong petroliferousodor...... 9 12 COVER: Mudstone and fossiliferousmudstone float ...... 12 ii FOSSILIFEROUS MUOSTONE: Slack (Ni)1 weathers to yellowish gray (5 V811); microcrystalline; thick, planarbeds with minor parallel, planarto slightly undulatory, flaggy splittinghabit, alternating with thin bedswith parallel, planar to slightly undulatory,laminated to predominantly fissilesplitting habit; minor, slightly undulatoryshaly partings between beds; sharp contactsbetween beds; 335 very thin, non-rhythmic, planar lamina commonly visible on weatheredsurface; "thick9 beds thinner overallthan those of unit 10; echinoidossicles, small brachiopod fragments, disarticulatod pelecypods, gastropods, ostracodes;fossils subparallel to bedding, randomly distributed; strong petroliferousodor; oily coating onsome fracture surfaces; subdued ledge-former; moderatelywell exposed ...... 17 10 FOSSILIFERDtJS MUDSTDNE: Grayish black (N2), weathers to mediumgray (N!); microcrystalline; thick tovery thick, planar beds with parallel,planar to slightly undulatory, flaggyto slabby, locally laminated, splittinghabit, alternating with thin tomedium beds with parallel, planar to rarelyslightly undulatory, fissile tolaminated splitting habit; sharp,. slightlyundulatory contacts between beds, planar contactsless common and typically at base ofthin/medium beds; extensively fractured; echinoidossicles and fragments, disarticulated pelecypods, few gastropods, ostracodes;most fossils parallel to bedding, randomlydistributed; strong petroliferous odor;subdued ledge-former; poorly tomoderately well exposed, but characterizedby many brief covered intervals ...... 66 FOSSILIFEROUS MUDSTONE: Dark brownish gray (5 YR 4/1), weathersto light gray (N7); microcrystalline; thick, planarbeds with parallel, slightly undulatory,flaggy splitting habit, alternatingwith medium beds with parallel,planar to slightly undulatory, fissile torarely laminated splitting habit; fewechinoid ossicles arid fragments, ostracodes,small brachiopod(?) fragments; fossilssubparallel to bedding, randomly distributed;strong petroliferous odor; very subduedledge-former; poorly to moderately well exposed ...... 20 8 FOSSILIFEROUS MUDSTONE: Grayish black (N2), weathers to yellowishgray (5 V /1); microcrystalline; thick topredominantly medium, planar beds withparallel, planar to slighlty undulatorylaminated to flaggy splitting habit, alternatingwith slightly silty, medium beds withparallel, planar to 336 slightly undulatory, laminatedto predominantly fissile splitting habit;few disarticulated and broken pelecypodsand small brachiopodsC),ostracodes; fossils subparallel to bedding, randomly distributed; strong petroliferousodor; subdued ledge-former; poorlyto moderately well exposed...... 42 7 FOSSILIFEROUS MUDSTONE: Grayish black (N2); weathers to medium lightgray (N6); microcrystalline; thick, planar bedswith parallel, planar slightlyundulatory, fiaggy splitting habit,alternating with medium beds with parallel,planar to undulatory, laminated topredominantly fissile splitting habit;very thin, planar lamjna visible on weatheredsurface; sharp contacts between beds; fewdisarticulated pelecypods, ostracodes; fossiis parallel to bedding, randomlydistributed; small burrows(?); strong petroliferousodor; subdued ledge-former; poorlyexposed...... 13 6 MUDSIONE: Black (Ni), weathers to yellowish gray (5 Y 8/1); microcrystalline;medium to thick, planar beds withparallel, planar to slightly undulatory,flaggy to slabby splitting habit,alternating with thin to medium beds withparallel, planar to slightly undulatory,fissile to laminated splitting habit;rare shaly partings; sharp, planar toslightly undulatory contacts betweenbeds; planar lemma locally visibleon weathered surfaces; few very small,indeterminate fossil fragments;many small, augen-shaped chert nodules; strongpetroliferous odor; subdued ledge-former; poorlyto moderately well exposed...... 17 S MUOSTONE: Dark gray (N3), weathers tovery pale orange (i YR 8/2); microcrystalline; parallel, planar medium bedswith parallel, slightly undulatory, flaggysplitting habit, alternating with thinto medium beds with parallel, planar toundulatory, laminated to predominantlyfissile splitting habit; sharp, planar toundulatory contacts between beds (where exposed);planar lamina visible on weathered surfacesof medium, flaggy beds; no fossilsvisible in outcrop; rare, small chert nodules; strong petroliferous odor; subduedledge-former...... 32 337 4 COVER: Moderate brown (5 YR 4/4) to moderate yellowish brown (1.0 YR 5/4) soil with sandstone float, passes upsect ion into light gray (N7) to mediumgray (N5) limestone talus field at base of northwest-facing ci iff/slope; represents transition from Kibbey Sandstone into Lombard Limestone...... 34 3 QUARTZ ARENITE: Very pale orange (5 YR 8/2) to yellowish gray (5 YR 4/4), weathersto moderate brown (5 YR 4/4) to grayish orange (10 YR 7/4); fine to medium grairsed; medium, planar to slightly undulatory beds; parallel, undulatory lamina locally visible in upper part; lower part massiveto mottled; iron-stained; subduedledge-former; only outcrop of Kibbey Sandstone...... 12 2 COVER: Gentle, grassy slope; small sandstone fragments common in upper 48 feet...... 250 COVER/SPRSELV FOSSILIFEROUS MUDSTONE: Med i urn greenish gray (5 6 5/1), weathers tomedium olive gray (5 Y 5/1); microcrystalline; crude, thick beds; thoroughly brecciated/fractured; few echinoid ossicles, brachiopod fragments, ostracodes; fossils randomly oriented and distributed;slightly recrystallized; very poorly exposed throughout grassy hillsideas small outcrops with very little relief; probablyMission Canyon Limestone...... unm. TDTPL (MAXIMUM): 1,109.0 feet (Base not exposed) 338 IV. SUNSET PEAK SECTION NW 1/4, SE 1/4, section 24, T.11 S.,R. 3 W., ntone Peak quadrangle, U.S.S.S. 7.3 minute series. Partial Lombard Limestone section measured in the saddle and on the southeast side of the hill (summit elevation 9,903') just northwest of Sunset Peak. The section traverse begins in the saddle between the hill and Sunset Peak, at the inferred Lombard-Amsden contact. This inferred contact is placed at the base of the stratigraphically lowest exposed sandstone rib (believed to be correlative to the Tyler Sandstone). Only the upper 391.3 feet of the Lombard Limestone are exposed here, as this interval has been thrust over by Mission Canyon Limestone, subsequent to or contemporaneous with folding and overturning. ll of the Paleozoic and Mesozoic units are overturned in this area. The northeast side of the hill is characterized by high Mission Canyon and Lodgepole Limestone cliffs. The Lombard is largely obscured or buried under talus shed from these overlying cliffs. The Lombard is variably exposed on the east-southeast side of the hill; talus from the Mission Canyon obscures a few intervals. The topographic expression of the uppermost Lombard, similar to that seen at Sawtooth and Hogback Mountains, suggests a buried shale/mudstone lithology in this uppermost stratigraphic interval. Some bed-on-bed fault thinning or thickening, obscured by talus, may have occurred within the exposed Lombard sequence, although this could not be substantiated. This area can be approached from the northeast or the west; the latter route is the shortest. To reach this location from the west, drive southeast from Blacktail Deer Creek road on FR 963 (along the east fork of Blacktail Deer Creek) to its end at Indian Creek. Hike southeast along the east fork of Blacktail Deer Creek to the confluence of Crows Nest Creek. Turn northeast and follow this creek to its origin just below the saddle by Sunset Peak. To approach the saddle from the northeast, drive to the "Notch" (see Hogback Mountain section), and hike southwest along Robb Creek until it turns east toward the saddle between Sunset and Olson Peaks. At this bend in the creek, continue south-southwest to the saddle northwest of Sunset Peak. 339 Unit Lithologv Ft. 19 SANDSTONE: Basal Amsden Formation; subdued ledge-former ...... unm. 18 COVER: Grassy; dark brownish gray (5 YR 3/1) soil; abundant fossiliferous wackstone, fossiliferous and non-fossiliferous mudstone float ...... 266 17 FOSSILIFEROUS WACKESTONE: Light olive gray (5 V 6/1), weathers to light brown (5 YR 6/1); finely crystalline (recrystallized); dolomitic; slightly silty; medium (few thick) undulatory beds with parallel, slightly undulatory to predominantly undulatory, flaggy to slabby splitting habit; undulatory, carbonaceous shale partings between beds; echinoid ossicles, disarticulated and broken pelecypods and brachiopods; most fossils subparallel to locally parallel to bedding, randomly distributed; many small, black, carbonaceous fragments and flakes, subparallel to bedding; extensively fractured; black (Ni) to brownish black (5 V 2/1) film locally on fracture surfaces; weak to moderate petroliforous odor; ledge-former...... iI.5 16 COVER: Grassy; fossiliferous wackestone and mudstone float ...... * ...... 26 15 FOSSILIFEROUS WACKESTONE/PACKSTONE: Brownish gray (5 YR 4/1), weathers to moderate yellowish brown (1 YR 5/4); finely crystalline (recrystallized); dolomitic; slightly silty to sandy; medium to thick beds with minor parallel, slightly undulatory to undulatory, flaggy to slabby splitting habit; slightly undulatory to undulatory carbonaceous shale partings between beds; few whole and many small disarticulated and broken brachiopods, few disart iculated pelecypods, ostracodes; most fossils subparallel to bedding; randomly distributed, stand with slight relief on weathered surface; many small carbonaceous fragments, subparallel to bedding; few medium beds with greater fossil density (packstones), anastomosing carbonaceous(?) filaments, very thin and thin undulatory lamina locally visible on weathered surface, abundant quart zose 340 silt; moderate petrol iferous odor; ledge-former ...... 11 14 COVER: Fossiliferous wackestone and mudstone float; minor non-fossiliferous mudstone float ...... 3 13 FOSSILIFEROUS WACKESTONE: Dark brownish gray (5 YR 3/1), weathers to moderate yellowish brown (10 YR 5/4); finely crystalline (recrystallized); dolomitic; slightly silty to sandy; medium beds with minor parallel, undulatory, flaggy splitting habit; slightly undulatory to undulatory, carbonaceous shale partings between beds; disarticulated and broken brachiopods and pelecypods(?), echinoid ossicles; fossils subparallel to bedding, randomly distributed; many small carbonaceous fragments, parallel to bedding; brownish black (5 V 2/1) film locally on fracture surfaces; moderate to strong petroliferous odor; ledge-former...... 6 12 COVER: Fossiliferous wackestone and mudstone float; also non-fossiliferous mudstone float...... , ...... 12 11 FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; medium beds with minor parallel, slightly undulatory, flaggy splitting habit, alternating with thin to medium beds with parallel, slightly undulatory, fissile to predominantly laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, disarticulated pelecypods, ostracodes; most fossils parallel to bedding, randomly distributed; many short, horizontal burrows; moderate to strong petroliferous odor; subdued ledge-former...... 9 10 COVER: Fossiliferous and non-fossiliferous mudstone float...... 4 9 FOSSILIFEROUS MUDSTONE: Grayish black (N2), weathers to light gray (N7); microcrystalline; medium to predominantly thick beds with parallel, planar to slightly undulatory, flaggy to slabby splitting habit, alternating with thin to medium beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting 341 habit; sharp, planar to locally slightly undulatory contacts between beds; some flaggy/slabby intervals pass laterally into fissile/laminated intervals; few echinoid ossicles and fragments, disarticulated and broken pelecypods and brachiopods, ostracodes; most fossils subparallel to bedding, randomly distributed; few short, horizontal to randomly oriented burrows; strong petroliferous odor; subdued ledge-former ...... * ...... 12 S COVER: Fossiliferous and non-fossiliferous mudstone float...... 4 7 FOSSILIFEROUS MUDSIONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; medium to thick beds with parallel, planar to slightly undulatory, slabby to locally flaggy splitting habit, alternating with medium beds with parallel to locally non-parallel, slightly undulatory, laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, disarticulated pelecypods and brachiopods, few ostracodes; fossils randomly oriented and distributed; moderate petroliferous odor; very subdued ledge-former; poorly exposed...... 6 COVER: Fossiliferous and non-fossiliferous mudstone float...... 3 5 FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; medium to thick beds with minor parallel, planar to slightly undulatory, flaggy to predominantly slabby splitting habit, alternating with thin to medium beds with parallel, slightly undulatory to undulatory, fisile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; few echinoid ossicles and fragments, disarticulated pelecypods and brachiopods(7), few broken gastropods(?); fossils parallel to bedding (except for ossicles which are randomly oriented), randomly distributed; few short, horizontal burrows; strong petroliferous odor; subdued ledge-former; fissile/laminated intervals poorly exposed ...... 11 342 4 COVER: Fossiliferous and non-fossiliferous mudstone float...... 5 3 FOSSILIFEROUS MUDSTONE: Grayish black (N2), weathers to medium light gray (N6); microcrystalline; medium to thick beds with parallel, slightly undulatory to locally planar, slabby splitting habit, alternating with thin and few medium beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; lower part of unit extensively fractured; sparsely fossiliferous; few echinoid ossicles, disarticulated and broken pelecypods and brachiopeds; most fossils subparallel to bedding, randomly distributed; strong petroliferous odor; subdued ledge-former...... 7 2 THRUST FAULT: Crush zone; variably sized Lombard Limestone and Mission Canyon Limestone fragments; thick, anastomosing fractures filled with coarse, milky calcite...... (2) DOLOMITIC LIMESTONE: Medium brownish gray (5 YR 5/1), weathers to medium gray (N!); recrystallized; extensively brecciated; very crude, very thick bedding; weak petroliferous odor; cliff-former; Thrust sliver of Mission Canyon Limestone...... unm. TOTAL: 391.5 feet 343 V. HO6BACI< MOUNTAIN SECTION SW 1/4, NE 1/4, and SE 1/4, section 6,1. 11 S., R. 4 W., Swamp Creek quadrangle, U.S.G.S. 7.5 minute series. Lombard Limestone section measured along a N 20°W traverse, from the northwestern side of the saddle in SE 1/4, SE 1/4, section 6 (between 9,328' hill and Hogback Mountain) to the inferred location of a down-north normal fault. The inferred position of this fault is based on a change in soil color from medium gray to brownish gray and/or a reddish brown color, the absence to noteworthy decrease in dark gray mudstone float, topographic expression, and the absence of any float indicative of Mission Canyon Limestone lithology. This fault was first suggested by Scheedlo (1984). The Lombard Limestone is best exposedon the northern side of the 9,328' hill. All of the exposed units are overturned, strike approximately N 55°E, and dip an average of 56°NW. The thick covered interval at the base of this section is probably thick asa result faulting, dip variations (increase in the degree of overturning), and/or a gentle to open parasitic fold on the overturned limb. To reach this area, called "The Notch", turn southwest from the Ruby River Road onto Ledford Creek Road. Drive approximately 3.7 miles to Robb Creek Road, then proceed approximately five miles to a cluster of small buildings CRobb Creek Association Headquarters on county map). Approximately 0.1 mile before the buildings a steep road branches to the northwest, up onto the bench adjacent to Robb Creek; do not attempt to take the road which begins on the northwest side of the fenced pasture adjacent to the buildings as it is deeply incised from gully erosion. Follow the road to the southwest, staying on the bench, to The Notch. It is advisable to confer with the local ranchers at the Robb Creek Association Headquarters regarding exact directions and the condition of the road. Beyond the ranch the road consists of two tire tracks which traverse several meadows, small hills, and streams. Drive to the southwest side of Hogback Mountain (SE 1/4, NE 1/4, section 6). To reach the saddle, hike approximately one mile east-northeast along the stream which empties into Robb Creek from the recent slide on the southwest side of Hogback Mountain. 344 Unit Litholoy Ft. 88 COVER: Grassy; shale float; measured to small bump/rib on west side of saddle (at base of 9,328' hill), presumed to represent basal Amsden Formation sandstone...... 86.5 87 SHALE: Black (NI), weathers to light gray (N7); microcrystalline; thin to medium bedded; beds parallel, planar; fissile to parallel, planar to slightly undulatory, flaggy splitting habit; degree of fissility varies laterally; very thin, parallel, slightly undulatory to disrupted lamina visible on weathered surface; non-fossiliferous; very strong petrol i ferous odor; slope-former to local ledge-former...... 77 86 COVER: Grassy; fossiliferous packstone float...... 32 85 BRACHIOPOD PACKSTONE: Dark yellowish brown (10 YR 4/2), weathers to medium brownish gray (5 YR 5/1); microcrystalline; thick beds with parallel, undulatory, slabby to blocky splitting habit, alternating with medium beds with parallel, undulatory, laminated to flaggy splitting habit; sharp, undulatory contact between thick and medium beds; disarticulated and broken brachiopods, echinoid ossicles, bryozoan debris, few ostracodes, broken pelecypods(?); fossils randomly oriented and distributed; few stylolites; weak petroliferous odor; ledge-former, medium beds less resistant...... 13 84 COVER: Grassy; dark gray soil; fossiliferous wackestone float...... 23 83 SPARSE BRYOZOAN WACKESTONE: Pale brown (5 YR 5/2), weathers to light gray (N7); microcrystalline; medium beds with parallel, slightly undulatory to undulatory, flaggy to slabby splitting habit, alternating with medium to predominantly thin beds with parallel, undulatory to slightly undulatory, fissile to laminated splitting habit; sharp to laterally gradational contact between thin, "platy" beds and subjacent medium, flaggy to slabby beds; sharp, planar to slightly undulatory contact between thin, "platy" beds and super,jacent medium, flaggy to slabby beds; trepostome and fenestrate bryozoan fragments, disarticulated and 345 broken brachiopods (few whole with geopetal fill), echinoid ossicles; mast fossils subparallel to bedding, randomly distributed; small chert nodules; moderate petroliferous odor; ledge-former...... 6 82 COVER: Grassy; medium gray soil; fossiliferous wackestone float...... 9 81 SPARSELY FOSSILIFEROUS WACKESTONE: Pale brown (5 YR 5/2), weathers to medium light gray (N6); microcrystalline; medium beds with parallel, slightly undulatory to undulatory, flaggy to slabby splitting habit, alternating with medium to predominantly thin beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; trepostome bryozoan fragments, disarticulated and broken brachiopods, echinoid ossicles and fragments; fossils randomly oriented and distributed; few small chert nodules; weak petroliferous odor; ledge-former...... 1ISI ...... 4 80 COVER: Grassy; fossiliferous wackestone float...... 13 79 FOSSILIFEROUS WflCKESTONE: Dark gray (P43), weathers to light gray (P47); microcrystalline; medium beds with minor parallel, planar to slightly undulatory, flaggy to slabby splitting habit, alternating with medium to predominantly thin beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; many echinoid ossicles and fragments, disarticulated and broken brachiopods, bryozoan fragments, ostracodes; fossils randomly oriented and distributed; bioturbated; burrows?; moderate petrol iferous odor; subdued ledge-former...... 3 78 COVER: Grassy; fossiliferous wackestone float...... 7 77 BRVOZON WPCKESTONE: Pale brown (5 YR 5/2), weathers to light gray (N7); microcrystalline; medium beds with parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with medium to predominantly thin beds with parallel, slightly undulatory, fissile to laminated 346 splitting habit; sharp, slightly undulatory contacts between beds; trepostome and fenestrate bryozoan fragments, disarticulatod and broken brachiopods, echinoid ossicles, broken pelecypods(?); most fossils subparallel to bedding, randomly distributed; burrows; few small chert nodules; very weak petroliferous odor; ledge-former...... 5 76 COVER: Grassy; medium gray soil; fossiliferous wackestone float...... * 12 75 FOSSILIFEROUS WPCKESTDNE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; medium beds with minor parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with medium to predominantly thin beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles and fragments, disarticulated and broken brachiopods, few bryozoan fragments; fossils randomly oriented and distributed; burrows; few small chert nodules; subdued ledge-former...... 3 74 COVER: Grassy; medium gray soil; fossiliferous wackestone float...... 6 73 FOSSILIFEROUS WACKESTONE: Dark olive gray (5 V 2/1), weathers to medium lightgray (N6); microcrystalline; thin to medium beds with parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with thin beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; many echinoid ossicles and fragments, few disarticulated brachiopods, ostracodes; fossils randomly oriented and distributed; bioturbated; moderate petrol iferous odor; ledge-former...... 4 72 COVER: Grassy; fossiliferous wackestone float...... 3 71 FOSSILIFEROUS WCKESTONE: Dark olive gray (5 V 3/1), weathers to lightgray (N6); microcrystalline; thin to medium beds with minor parallel, slightly undulatory, flaggy to slabby splitting habit, alternatingwith thin beds with parallel, planar to slightly undulatory, fissile to laminated splitting 347 habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, disart iculated and broken brachiopods, ostracodes(?), bryozoan debris; fossils randomly oriented and distributed; burrows; small chart nodules; moderate petroliferous odor; ledge-former ...... 2 70 COVER: Grassy; medium gray soil; scattered fossiliferous wackestone float ...... 4 69 SPARSELY FOSSILIFEROUS WACKESTONE: Olive black (5 V 2/1), weathers to medium light gray (NE); microcrystalline; medium beds with minor slabby splitting habit, alternating with medium beds with parallel, planar to undulatory, fissile to laminated splitting habit; contact at top of fissile/laminated beds sharp and undualtory (up to 2" relief); contact at base of same beds sharp, planar to slightly undulatory; echinoid ossicles, whole (few) and disarticulated brachiopods, disarticulated pelecypods, few bryozoan fragments; horizontal burrows; fossils randomly oriented and distributed; moderate petroliferous odor; ledge-former...... 6 68 COVER: Grassy; fossiliferous wackestone and rnudstone float ...... 7 67 FOSSILIFEROUS WACKESTONE: Olive black (5 Y 2/1), weathers to medium gray (N5); microcrystalline; medium beds with minor slabby splitting habit, alternating with medium beds with parallel, planar to undulatory, fissile to laminated splitting habit; contacts at top of fissile/laminated beds sharp and undulatory (1" to 2" relief); contacts at base of same beds sharp and slightly undulatory; echinoid ossicles, disarticulated brachiopods and pelecypods, small indeterminate horn corals, scattered bryozoan fragments; fossils randomly oriented and distributed; moderate petroliferous odor; ledge-former...... 4 66 COVER: Grassy; medium gray soil; scatterd fossiliferous wackestone and mudstone float...... 12 65 SPARSELY FOSSILIFEROUS WACKESTONE: Dusky brown (5 YR 2/2), weathers to medium gray (N5); microcrystalline; medium to thick beds with minor slabby splitting habit, alternating with thin to medium beds with 348 parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory (<1" relief) contacts between beds; echinoid ossicles, disart iculated brachiopods and pelecypods, few small indeterminate corals, scattered bryozoan fragments; fossils randomly oriented and distributed; moderate petrolifarous odor; ledge-former...... 8 64 COVER: Grassy; medium gray soil; scattered fossiliferous wackestone and mudstone float...... S 63 SPRRSELV FOSSILIFEROUS WCKESTONE: Dusky brown(5 YR 2/2),weathers to medium gray (NS); microcrystalline; medium to thick beds with minor slabby splitting habit, alternating with thin to medium beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory ((1U relief) contacts between beds; echinoid ossicles, disart iculated brachiopods, scattered bryozoan fragments; fossils randomly oriented and distributed; moderate petroliferous odor; ledge-former...... 3 62 COVER: Grassy; medium gray to medium light gray soil; fossiliferous wackestone float...... 14 61 FOSSILIFEROUS WCKESTDNE: Olive black (5 V 2/1),weathers to medium light gray (N6); microcrystalline; thick beds with rare slabby to blocky splitting habit, alternating with medium beds with parallel to non-parallel, slightly undulatory, fissila to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, disarticulated and broken brachiopods and pelecypods, few bryozoan fragments, few ostracodes(?); fossils randomly oriented and distributed; weak petroliferous odor; ledge-former...... 2 6 COVER: Grassy; medium gray soil; fossiliferous wackestone and mudstone float...... 6 59 SPflRSELY FOSSILIFEROUS WPCKESTONE: Olive gray (S V 211), weathers to medium lightgray (N6);microcrystalline; medium to predominantly thick beds withrare slabby splitting habit, alternating with thinto medium beds with parallel tonon-parallel, 349 slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles and fragments, disarticulated and broken brachiopods and pelecypods, bryozoan fragments; fossils randomly oriented arid distributed; weak petroliferous odor; ledge-former...... S 58 COVER: Grassy; fossiliferous wackestone float...... 3 57 FOSSILIFEROUS WACKESTONE: Dark olive gray (5 Y 3/1), weathers tovery light olive gray (5 V 7/1); microcrystalline; thick beds with rare slabby splitting habit, alternating with medium beds with parallel to non-parallel, slightly undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, disarticulated and broken brachiopods and pelecypods(?), bryozoan fragments; fossils randomly oriented and distributed; weak to moderate petroliferous odor; ledge-former...... 4 56 COVER: Grassy; fossiliferous wackestone and packstone float...... 7 55 PELECYPOD PACKSIONE: Brownish black (5 YR 2/1), weathers to light olivegray (5 V 6/1); microcrystalline; mediumbeds with minor flaggy to slabby splitting habit; rare, thin shaly partings; whole and disarticulated (few broken)pelecypods, disarticulated brachiopods, gastropods, trilobites, few fenestrate bryozoan fragments; fossils randomly oriented and distributed; moderate petroliferous odor; verysubdued ledge-former...... 2 54 COVER: Grassy; fossiliferous wackestone and packstone float, some raudstone float...... 5 53 PELECYPOD PACKSTONE: Brownish black (5 YR 2/1), weathers to light olivegray (3 V 6/i); microcrystalline; mediumbeds with minor flaggy to slabby splitting habit; thin, shaly partings; wholeand disarticulated pelecypods, disarticlated brachiopods, gastropods; fossils randomly oriented and distributed; moderate petroliferous odor; very subtle ledge-former; poorly exposed...... 2 350 52 COVER: Grassy; fossiliferous wackestone arid packstone float, some mudstorie float...... 16 51 FOSSILIFEROUS PACKSIONE: Brownish black (5 YR 2/1), weathers to light olive gray (5 V 6/1); microcrystalline; medium beds with minor slabby splitting habit; rare, thin shaly partings; whole (few) and disarticulated pelecypods, disarticulated brachiopods, gastropods, bryozoan fragments; fossils randomly oriented and distributed; moderate petroliferous odor; very subdued ledge-former; poorly exposed...... 3 $0 COVER: Grassy; fossiliferous wackestone and packstone float, some mudstone float ...... 8 49 SPARSELY FOSSILIFEROUS WACKESTONE: Dusky brown (5 YR 2/2), weathers to mediumgray (N$); microcrystalline; medium beds with minor flaggy to slabby splitting habit; thin, shaly partings; disarticulated brachiopods and pelecypods, echinoid ossicles; fossils randomly oriented and distributed; moderate petroliferous odor; subdued ledge-former...... 3 48 COVER: Grassy fossiliferous wackestone float...... 4 47 SPARSELY FOSSILIFEROUS WACKESTONE: Dusky brown (5 YR 212), weathers to mediumgray INS); microcrystalline; medium bed with minor flaggy to slabby splitting habit; disart iculated brachiopods and pelecypods, echinoid ossicles and fragments; fossils randomly oriented and distributed; moderate petrol i ferous odor; subdued ledge-former...... 1 46 COVER: Grassy; medium light gray soil; fossiliferous wackestone and mudstone float...... 3$ 45 BRYOZOAN PACKSTONE: Olive gray (5 V 4/1) to brownish black (5 YR 2/1), weathers to pale grayish orange (10 YR 8/4); microcrystalline; medium beds with parallel, planar to slightly undulatory, flaggy splitting habit, alternating with thin beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, planar contact betweenmedium beds and superjacent thin beds; sharp, planar to undulatory contact between medium hin beds; dendroid, 351 indeterminate trepostome and rhal3domesid bryozoans, disart iculated brachiopods, echinoid ossicles and fragments, ostracodes; most fossils parallel to bedding, randomly distributed; moderate petroliferous odor; subdued ledge-former...... 3 44 COVER: Grassy; fossiliferous wackestone and packstone float...... 4 43 ECHINOID-BRYOZOflN PCKSTONE: Olive gray (5 V 4/1), weathers tovery light gray (N8) to very pale orange (1 YR 812); microcrystalline; medium beds with parallel, slightly undulatory, flaggy splitting habit, alternating with thin beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles (including pentacrinus) and fragments, dendroid, indeterminate trepostome, rhabdomesid, and fenestrata bryozoans, disart iculated brachiopods, ostracodes; most fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; subdued ledge-former...... 3 42 FOSSILIFEROUS WCKESTONE: Dark olive gray (5 V 3/1), weathers tovery light olive gray (5 V 7/1); microcrystalline; medium beds with parallel, slightly undulatory, flaggy splitting habit, alternating with very thin to thin beds with parallel, slightly undulatory, laminated to predominanatly fissile splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, disart iculated brachiopods, bryozoan fragments, ostracodes(?);most fossils parallel to bedding, randomly distributed; moderate petroliferous odor; ledge-former; sharp, slightly undulatory to undulatory contacts betweenunits 41 and 43...... 2 41 ECHINOID-BRVOZOPN PCKSTONE: Olive gray (5 V 4/1), weathers tovery light gray (N8); microcrystalline; mediumbeds with parallel, planar to slightly undulatory, flaggy splitting habit, alternatingwith very thin to thin beds with parallel, slightly undulatory fissile to laminated p, slightly undulatory 352 contacts between beds; echirioid ossicles (including Pentacrinus) and fragments, indeterminate dendroid t repastame and fenestrate bryozoans, disart iculated brachiopods; most fossils subparallel to bedding; moderate petroliferous odor; subtle ledge-former; sharp, planar contact with unit 40...... 2 40 FOSSILIFEROUS WCKESTDNE: Dark olive gray (5 V 3/1), weathers to lightgray (N7); microcrystalline; medium to thick beds with parallel, planar tovery slightly undulatory, slabby to blocky splitting habit, alternating withvery thin to thin beds with parallel, slightly undulatory, laminated to predominantly fissile splitting habit; sharp, slightly undulatory contacts between beds; shaly partings between beds lesscommon; echinoid ossicles and fragments, disarticulated and broken brachiopods, few bryozoan fragments; fossils subparallel to bedding, randomly distributed; many chert nodules and stringers (up to 10" long and 4" high); weak to moderate petroliferous odor; ledge-former...... 8 39 COVER: Grassy; fossiliferous wackestone and mudstone float...... 3 38 SPPRSELV FOSSILIFEROUS WCRESTONE: Olive black (5 V 2/1), weathers to yellowishgray (5 V 8/1); microcrystalline; mediumto thick beds with parallel, planar tovery slightly undulatory, slabby to blocky splitting habit, alternating with very thin to thin beds with parallel, slightly undulatory, laminated to predominately fissile splitting habit; sharp, planar to slightly undulatory contact between beds; echinoid ossicles, disarticulated brachiopods, few bryozoan fragments; most fossils parallel to bedding; many chert nodules andstringers (up to 14" long and 3" high); moderate petroliferous odor; ledge-former...... 3 37 FOSSILIFEROUS WCKESTONE: Dark gray (N3), weathers to light olivegray (3 V 6/1); microcrystalline; thick bed with minor parallel, planar to slightly undulatory, slabby splitting habit, betweentwo medium beds with parallel, planarto 353 slightly undulatory, laminated tolocally fissile splitting habit; sharp,planar to slightly undulatory contacts between beds and between medium, laminated bedsand units 36 and 38; echinoid ossiclesand partial stems, whole and disarticulated brachiopods; most fossils subparallelto bedding, randomly distributed; moderate petroliferous odor; medium, laminatedbeds poorly exposed; ledge-former...... 2 36 SPPRSELY FOSSILIFEROUS WCKESTONE: Olive black (5 V 2/1), weathers toyellowish gray (5 V 8/1); microcrystalline; medium to thick beds with parallel,planar to very slightly undulatory, slabby to blocky splitting habit, alternating withthin to medium beds with parallel, slightly undulatory, fissile to laminatedsplitting habit; sharp, planar to slightlyundulatory contacts between beds; echinoidossicles, disarticulated brachiopods, fewbryozoan fragments, ostracodes(?); mostfossils parallel to bedding, randomly distributed; few small chert nodules; weakto moderate petroliferous odor; ledge former...... 4 35 COVER: Grassy; fossiliferous wackestoneand mudstone float...... 8 34 SPRSELV FOSSILIFEROUS WCKESTONE: Olive black (5 V 2/1), weathers toyellowish gray (5 V 8/1); microcrystalline; medium beds with minor parallel,planar to slightly undulatory, flaggyto slabby splitting habit, alternating withthin to medium beds with parallel,slightly undulatory, fissile to laminatedsplitting habit; sharp, planar to slightly undulatory contacts between beds;echinoid ossicles and fragments,disarticulated and broken brachiopods, few bryozoanfragments, ostracodes; most fossils parallelto bedding, randomly distributed;moderate petroliferous odor; sharp, slightly undulatory contact with unit 33; ledge-former...... 3 33 BRCHIOPOD PCKSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; thin bed, with minor parallel, slightlyundulatory, laminated splitting habit;many whole and disarticulated brachiopods,few 354 pelecypods, echinoid ossicles and fragments, ostracodes; most fossils subparallel to bedding, randomly distributed; weak petroliferous odor; ledge-former...... 0. 3 32 BRACHIOPOD WCKESTONE: Dark gray (N3), weathers to light olivegray (5 V 6/1); microcrystalline; medium to thick beds with minor parallel, planar toslightly undulatory, slabby to blocky splitting habit; few thin to medium bedswith parallel, planar to slightlyundulatory, fissile topredominantly laminated splitting habit; shaly partingsbetween medium to thick bedsmore common; many disarticulated and few whole brachiopods, echinoid ossicles and few partialstems, few bryozoan fragments,ostracodes(?); most fossils parallel to subparallelto bedding, randomly distributed; moderate petroliferous odor; subtle to good ledge-former, poorly to moderately well exposed...... 10 31 COVER: Grassy; fossiLiferous wackestone and mudstone float...... 8 30 FOSSILIFEROUS WCKESTONE: Dark gray(N3), weathers to light olivegray (5 V 6/1); microcrystalline; medium beds with minor parallel, slightly undulatory,flaggy splitting habit; beds separatedby shaly parting; echinoid ossicles andpartial stems, disarticulated brachiopods,solitary corals (including Siphonohylliasp.), few bryozoan fragments; most fossils subparallel to bedding, randomly distributed; moderate petroliferousodor; subdued ledge-former...... 1.5 29 COVER: Grassy; fossiliferous wackestoneand mudstone float...... 2 28 FOSSILIFEROUS WCKESTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; medium to thickbeds with minor parallel, planarto slightly undulatory, flaggy to slabbysplitting habit, alternating withvery thin to thin, beds with parallel, slightlyundulatory, fissile to laminated splittnghabit; sharp, slighity undulatory contactsbetween beds; echinoid ossicles and fragments, 355 disarticulated brachiopods, few small solitary corals, few bryozoan(?)fragments; fossils subparallel to bedding, randomly distributed; weak to moderate petroliferous odor; ledge-former; gradational contact with unit 27...... 27 BRCHIOPOD PCKSTONE: Medium dark Gray (N4), weathers to light olivegray (5 V 611); microcrystalline; thin bed with parallel, slightly undulatory, laminatedsplitting habit (progressively less significantnear upper and lower part of bed); transitional contact with units 26 and 27; wholeand disarticulated brachiopods, echinoid ossicles and fragments, ostracodes,few disarticulated and broken pelecypods(?); most fossils subparallel tobedding, randomly distributed; weakpetroliferous odor; subdued ledge-former...... 3 26 FOSSILIFEROUS WACKESTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; thick bed with minor parallel, planar to slightlyundulatory, flaggy to slabby splitting habit, underlain by thin(?) bed with parallel, planar to slightly undulatory,fissile splitting habit; sharp, planarto slightly undulatory contact between beds;echinoid ossicles and fragments, disarticulated brachiopods; fossils subparallel to bedding, randomly distributed;moderate petrol iferous odor; ledge-former...... 1 25 COVER: Grassy; fossiliferous wackestoneand raudstone float...... 16 24 FOSSILIFEROUS WACKESTONE: Dark gray (N3), weathers to medium lightgray (N6); microcrystalline; medium to thickbeds with minor parallel, planarto very slightly undulatory, flaggy to predominantly slabby splitting habit, alternating with thin to rarelymedium beds with parallel, planar toslightly undulatory, laminated to locallyfissile splitting habit; sharp,very slightly undulatory contacts between beds;echinoid ossicles and fragments, disarticulated brachiopods, ostracodes('),fewbryozoan fragments; most fossils subparallelto bedding; moderate petroliferous odor; subtle ledge-former; poorlyexposed...... 3 356 23 COVER: Grassy; mudstone, fossiliferous mudstorieand wackestone float...... 3 22 FOSSILIFEROUS MUDSTDNE: Black (Ni), weathers to yellowish gray (5 V8/i); microcrystalline; medium beds withvery minor parallel, slightlyundulatory, flaggy to slabby splitting habit;slightly undulatory shaly partingbetween beds; disarticulated brachiopods, few indeterminate bryozoan fragments;fossils randomly oriented anddistributed; strong petroliferous odor; subduedledge-former...... 2 21 COVER: Grassy; medium darkgray to dark brownish gray soil; mudstoneand fossiliferous mudstone float ...... 5 20 FOSSILIFEROUS MLJDSTONE: Black (Ni), weathers to yellowish gray (5 V8/i); microcrystalline; thick to predominantly medium beds withvery minor parallel, planar to very slightlyundulatory splitting habit; planar toslightly undulatory shaly partingsbetween beds; rare thin bed with parallel, planarto slightly undulatory, fissileto laminated splitting habit; echinoidossicles and few partial stems, disarticulatedbrachiopods, few bryozoan fragments;fossils subparallel to bedding, randomly distributed; strong petroliferousodor; 1 edge-former...... 7 19 COVER: Grassy; dark brownishgray soil; mudstone and fossiliferousmudstone float...... 4 18 FOSSILIFEROUS MLJDSTONE: Grayish black (N2), weathers to yellowishgray (5 V 8/1); microcrystalline; medium beds(lacking any internal splitting habit),separated by slightly undulatory shalypartings; echinoid ossicles, disarticulated brachiopods, few bryozoan(?)fragments; fossils randomly orientedand distributed; moderate to strong petroliferousodor; ledge-former ...... 2 17 COVER: Grassy; medium darkgray (N4) soil; fossiliferous mudstone andpackstone float...... 6 16 FOSSILIFEROUS PACKSIONE: Dark olive gray (5 V 3/1), weathers tolight gray (N7); microcrystalline; thickbed with very minor 357 parallel, slightly undulatory, flaggy to slabby splitting habit; echinoid ossicles, and partial stems, whole and disarticulated pelecypods and brachiopods, bryozoan debris, few gastropods, disarticulated trilobites; fossils subparallel to bedding, randomly distributed, stand with excellent relief on weathered surface; strong petroliferous odor; subdued ledge-former; sharp, slightly undulatorycontactwithunitl5 ...... 1 15 FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; two medium beds with parallel, planar to slightly undulatory, flaggy splitting habit, alternating with very thin to thin beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp contact between beds; echinoid ossicles and fragments, disarticulated brachiopods, few pelecypods(?), ostracodes; fossils subparallel to bedding, randomly distributed; strong petroliferous odor; subdued ledge-former; sharp, planar to slightly undulatory contact with unit 14 ...... 2 14 FOSSILIFEROUS PCKSTDNE: Dark olive gray (5 V 3/1), weathers to light gray (N7); microcrystalline; medium and thick beds with minor parallel, slightly undulatory flaggy to predominantly slabby splitting habit, alternating with very thin to thin beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory to rarely planar contacts between beds; echinoid ossicles (including Pentacrinus) and partial stems, few whole and many disart iculated pelecypods and brachiopods, bryozoan fragments; most fossils subparallel to bedding, randomly distributed; very strong petroliferous odor; subdued ledge-former; sharp, slightly undulatorycontact with unit 13 ...... 2 13 FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; medium bed with parallel, planar to slightly undulatory, laminated splitting habit; echinoid ossicles, disarticulated brachiopods, few pelecypods(?); most fossils parallel to bedding, randomly distributed; very strong 358 petroliferous odor; subdued ledge-farmer, but less resistant than units 12 and14; sharp, slightly undulatory contact with unit 12...... 12 FOSSILIFEROUS MLJDSTONE: Dark gray CN3), weathers to medium lightgray (N6), microcrystalline; medium bed withvery minor parallel, planar to slightly undulatory, flaggy splitting habit; echinoid ossicles, disarticulated brachiopods, ostracodes(?); fossils subparallel to bedding, randomly distributed; strong petroliferous odor; subdued ledge-former...... 1 11 COVER: Grassy; medium gray to lightgray soil; fossiliferous wackestone and mudstone float...... 24 1 SPRSELV FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to mediumgray (N5); microcrystalline; thin to medium beds with minor parallel, slightly undulatory,flaggy splitting habit; beds separatedby slightly undulatory to undulatory, shaly partings; few echinoid ossicles; randomlyoriented and distributed; strong petroliferousodor; very subdued ledge-former; poorly exposed; sharp, undulatory (2" to 3" relief)contact (largelyobscurred)withunit9...... 2 9 FOSSILIFEROUS WC}(ESTONE:Dark olive gray (5 V 3/1), weathers to lightolive gray (5 V 611); microcrystalline;medium and thin beds with minor parallel,slightly undulatory, flaggy splitting habit;beds separated by slightly undulatory shaly parting; echinoid ossicles and few partial stems, disarticulated brachiopods,bryozoan fragments, disarticulated trilobites, gastropods; fossils randomly orientedand distributed; strong potroliferous odor; ledge-former...... 1 8 COVER: Grassy; fossiliferous wackestone and mudstone float...... 1.5 7 BRYOZOP4-CORL PCKSTONE: Olive gray (5 V 4/1), weathers tovery light gray (N8); microcrystalline; mediumbeds with very minor parallel, slightly undulatory, flaggy splitting habit; bedsseparated by 359 undulatory shaly parting; fenestrateand trepostome bryozoan debris, solitarycorals (including Michelinia cf. meekana Girty), echinoid ossicles, and partialstems, disarticulated brachiopods; most fossils subparallel to bedding, randomly distributed; weak petroliferous odor; ledge-former; sharp, undulatory contact with unit 6...... 2 6 FOSSILIFEROUS WCKESTONE: Dark olive gray (5 V 3/1), weathers to lightolive gray C! V 5/1); microcrystalline;thin to medium beds with very minor to minor, parallel, slightly undulatory, flaggy splitting habit; beds separated by slightly undulatory shaly partings and rare very thin to thin beds with parallel, planar to slightly undulatory,laminated to fissile splitting habit;sharp contacts between beds; echinoid ossicles andfew partial stems, bryozoan debris, disarticulated trilobites, indeterminate orthoconic nautiloid fragments, whole and disarticulated brachiopods; most fossils subparallel to bedding, randomly distributed; strong petroliferous odor; ledge-former...... 5 5 COVER: Grassy; fossiliferous wackestone and minor mudetone float...... 2 4 FOSSILIFEROUS WACKESTONE: Dark olive gray (5 V 3/1), weathers to lightolive gray (5 V 5/1; microcrystalline; thinand medium beds with very minor parallel,slightly undulatory, flaggy splitting habit, alternating with very thin beds with parallel, planar to slightlyundulatory, fissile to laminated splittinghabit; echinoid ossicles, many disarticulated and few whole brachiopods, bryozoandebris, few gastropods; fossilssubparallel to. bedding; moderate petroliferousodor; subdued ledge-former...... 2. 5 3 COVER: Grassy; medium darkgray soil; fossiliferous mudstone float...... 65 2 FOSSILIFEROUS MUDSTONE: 2rownish black (5 YR 2/1), weathers tolight gray (N7); microcrystalline; medium to few thinbeds, lacking internal splittinghabit; randomly fractured; separated by planarto slightly 360 undulatory, shaly partings; echinoid ossicles and partial stems,ostracodes; fossils randomly oriented anddistributed; horizontal burrows; indeterminatetrace fossils on bedding planes; small, augen-shaped to spherical chert nodules; very strong petroliferous odor;very subdued ledge-former; poorly exposed...... COVER: Orassy; dark gray soil; fossiliferous and non-fossiliferous mudstonefloat; probably structurally thickened;measured to inferred normal fault...... 1. 087 TOTAL: 1,801.3 feet 361 VIA. SLIDEROCK MOUNTAIN SECTIONI SW 114, SW 114, section 24,and NW 1/4, NW 1/4, section 23, T. 10 5., R. 4 W., Spur Mountain quadrangle,U.S.G.S. 7.3 minute series. Partial Lombard Limestone sectionmeasured along two west-east traverses,separated by a 680 foot offset 120 feet above the base of thesection. The Paleozoic and Mesozoic units east of SliderockMountain are all vertical to overturned. A thrust fault separatesthese overturned units from the right-side-up units in and west ofSliderock Mountain. This fault juxtaposesa thin sliver of the upper, part of the Amsden Formation against theupper part of the Lombard; the uppermost Lombard shales and mudstoneare faulted out. The lower boundary of this Lombardexposure is controlled by a second thrust fault characterized by much lessvertical separation than the other, displaying no more than 100 feetof separation (Scheedlo, 1984). Two smaller thrust faultsparallel, and probably splay from, the second thrust fault. Although the uppermost andlowermost parts of the Lombard are faulted out or covered, the complete,unfaulted, medial section can be measured alongtwo traverses. The lower 120 feet (units 1-12) were measuredon the west-northwest facing cliffs at the southeast end of thelarge amphitheater, at the northern end of Sliderock Mountain. The upper 461 feet were measuredon the knob at the base of the eastside of Sliderock Mountain, between the heads of Fawn Creek andDry Fawn Creek. A small saddle divides this knob into twosmaller knobs, and may represent another thrust fault, althoughthere is no indication of sucha fault in exposures to theimmediate north and south. Sliderock Mountain can onlybe approached by foot or helicopter. Drive south from Alder, along RubyRiver Road (FR 100) to Cottonwood Campground. Continue approximately 4.3 miles to a location midway between Dry Fawn Creek and Dog Creek. Park, cross the Ruby River, and hike northweston the gentle, eastward-dipping bench toward thelarge, recent landslide on the east side of Sliderock Mountain. Hike along the northern edge of the landslide to the base ofthe cliffs, turn north, and continue to the west-facing cliffs atthe southeast side of the amphitheater. Note the well exposed, west-dippingthrust fault and east-verging roll-overstructure on the north side of the amphitheater. 362 Unit Lithaloy Ft. 49 SANDSTONE/DOLOMITE: Upper part of Amsden Format ion (msden Fra. -QuadrantFm. transition); medium to thick bedswith intermittent covered intervals...... unm. 48 COVER: Grassy; thrust fault...... I 47 FOSSILIFEROUS WACKESTONE: Olive black (5 V 2/1), weathers tolight gray (N7); microcrystalline; thick to predominantly medium beds with minor parallel,planar to slightly undulatory, flaggysplitting habit, alternating with thinto medium calcareous shale beds; sharp,planar to slightly undulatory contactsbetween beds; echinoid ossicles, disarticulatedand broken brachiopods, fewindeterminate bryozoan fragments, gastropods;fossils randomly oriented and distributed; fractured; strong petroliferousodor; very subdued ledge-former; shaleinterbeds poorly exposed...... 48 COVER: Grassy; fossiliferous wackestonefloat...... 7 45 FOSSILIFEROUS WACKESTONE: Olive black (5 V 2/I), weathers tolight gray (N7) to light bluish gray (5 B7/1); microcrystalline; thin to mediumbeds with parallel, slightlyundulatory, laminated to flaggy splittinghabit, alternating with medium topredominantly thin, calcareous shalebeds; sharp, planar to slightly undulatorycontacts between beds; echinoid ossicles,disarticulated and broken brachiopods,indeterminate small horn corals(?);ostracodes, gastropods; fossils randomlyoriented and distributed; fossils locallysubparallel to bedding, associatedwith faint, undulatory, thin lamina visibleon weathered surface; few thinbrachiopod packstone beds; extensivelyfractured; very strong petroliferous odor;very subdued ledge-former; poorlyto locally moderatelywell exposed...... 11 44 COVER: Grassy; fossiliferouswackestone and m udstone float ...... 3 43 FOILIFEROUS WC}(ETONF2 Olive black Light gray (N7) to 363 very light olive gray (5 V 7/1); microcrystalline; medium beds with parallel, planar to slightly undulatory, laminated to flaggy splitting habit; few thin, calcareous shale interbeds; echinoid ossicles, few disarticulated and many broken brachiopods, gastropods, ostracodes, few indeterminate bryozoan fragments; fossils randomly oriented and distributed; extensively fractured; very strong petroliferous odor; very subdued ledge-former ...... 7 42 COVER: Grassy; Fossiliferous wackestone and packstone float ...... 3 41 FOSSILIFEROUS PCKSTONE: Light olive gray (5 V 6/1), weathers to light gray (Ni); microcrystalline; no discernable bedding (one thick bed?); parallel, slightly undulatory, flaggy splitting habit; echinoid ossicles, broken brachiopods, indeterminate bryozoan fragments, ostracodes, gastropods; fossils randomly oriented and distributed; minor vuggy porosity along fractures, both with local brownish blackC 5 YR 2/1) stain; weak to moderate petroliferous odor; subdued ledge-former; poorly exposed ...... 3 40 FOSSILIFEROUS MUDSTONE: Very dark yellowish brown (10 YR 3/2), weathers to light gray (Ni); microcrystalline; very thin to medium beds, some with parallel, slightly undulatory to undulatory, flaggy splitting habit, alternating with parallel, planar to slightly undulatory, fissile to predominantly laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; sparsely fossiliferous; echinoid ossicles, disarticulated and broken pelecypods and (few) brachiopods, ostracodes; fossils subparallel to bedding, randomly distributed; few stylolites; very strong petroliferous odor; poorly exposed upper contact with unit 41 ...... 3 39 SPRSELV FOSSILIFEROUS WCKESTONE: Olive gray (5 V 4/1), weather to medium light gray CN6) to yellowish gray (5 V 7/2); microcrystalline; thick to very thick massive beds, alternating with thin to medium beds with parallel, slightly 364 undulatory to undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; disarticulated arid broken brachiopods, many foraminifera, echinoid ossicles, gastropods, ostracodes; fossils randomly oriented and distributed; vuggy porosity along fractures, both with common brownish black (5 V 2/i) stain; strong petroliferous odor; pronounced ledge-former; sharp, undulatory contact with unit 40 ...... 9 38 BRCHIOPOD PCKSTONE: Light olive gray (5 V 5/2), weathers to greenish gray (5 BY 6/i); microcrystalline; medium bed with parallel, slightly undulatory, flaggy splitting habit; predominantly disarticulated and few whole Orthotacean (Strophominidae?) brachiopods, few echinoid ossicles; most fossils parallel to bedding, randomly distributed, tightly packed; very weak petroliferous odor; subdued ledge-former; sharp, slightly undulatory contact with unit 39 ...... 2 37 FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to very light olive gray (5 V 7/1); microcrystalline; medium to thick beds with very minor, discontinuous, parallel, planar to slightly undulatory, flaggy to slabby splitting habit, alternating with very thin to thin, calcareous shale beds; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles, disarticulated and broken brachiopods, ostracodes, indeterminate bryozoan fragments; fossi Is randomly oriented and distributed; weak to moderate petroliferous odor; subdued ledge-former; sharp, slightly undulatory contact with unit 38 ...... 6 36 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/i), weathers to light olive gray (5 V S/i); microcrystalline; thin beds with slightly undulatory, calcareous shale partings; predominantly echinoid ossicles and fragments, finely broken brachiopods, ostracodes; fossils randomly oriented and distributed, locally clustered; faint, swirled to irregular patchy texture (bioturbation) on weathered surface; brownish black (5 V 2/1) stain on some fracture surfaces; strong petroliferous 365 odor; extensively fractured; subdued ledge-former; sharp, planar to slightly undulatory contacts with units 35 and 37 ...... 3 33 COVER: Grassy; fossiliferous wackestone float ...... 3 34 FOSSILIFEROUS WCKESTONE: Olive gray (5 V 4/1), weathers to very light olive gray (5 V 7/1); microcrystalline; medium to thick beds with very minor, discontinuous, parallel, slightly undulatory, slabby splitting habit, alternating with very thin to medium, calcareous shale beds; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles, disarticulated and few broken brachiopods, small horn corals(?), indeterminate ramose bryozoan fragments (up to 1/2" long); fossils randomly oriented and distributed; short, horizontal to inclined burrows; moderate petroliferous odor; few stylolites; ledge-former ...... 13 33 COVER: Grassy; fossiliferous wackestone float...... 7 32 FOSSILIFEROUS WCKESTONE: Olive gray (3 V 4/1), weathers to very light olive gray (3 V 7/1); microcrystalline; thick beds with very minor, discontinuous, parallel, slightly undulatory to locally undulatory, slabby splitting habit, alternating with thin to medium, calcareous shale beds; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, disarticulated and broken brachiopods (including indeterminate Spiriferids(?) and Productids), few ostracodes, few fenestrate and indeterminate bryozoan fragments, small horn corals(); fossils randomly oriented and distributed; weak petroliferous odor; ledge-former ...... S 31 COVER: Grassy; fossiliferous wackestone float ...... 2 30 FOSSILIFEROUS WflCI(ESTONE: Olive gray (5 V 4/1), weathers to very light gray (N8);microcrystalline; medium and few thick beds with very minor, parallel, slightly undulatory, flaggy splitting habit, alternating with very thin to few thin, calcareous shale beds; sharp, planar to locally slightly undulatory contacts between beds; echinoid ossicles, disarticulated and few broken brachiopods, 366 few indeterminate bryozoan fragments, ostracodes, foraminifera; fossils randomly oriented and distributed; pelletsY?); few stylolites; short, horizontal to inclined burrows; moderate petroliferous odor; 1 edge-former...... ii 29 COVER: Brassy; fossiliferous wackestone and ruudstone float ...... 23 28 FOSSILIFEROUS WAC}(ESTONE: Dark olive gray (5 V 3/1), weathers to light gray (N7); microcrystalline; medium beds, alternating with very thin to thin, calcareous shale beds; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles, disarticulated and few broken brachiopods, few indeterminate bryozoan fragments, ostracodes; fossils randomly oriented and distributed; weak petroliferous odor; ledge-former...... 4 27 COVER: Brassy; scattered fossiliferous and non-fossiliferous mudstone float; dark brownish gray (5 V 3/1) soil; saddle-former ...... 171 26 FOSSILIFEROUS MUDSTONE: Dark olive gray (5 V 3/1), weathers to light gray (N7); microcrystalline; medium to thick beds with minor parallel, planar to slightly undulatory, flaggy splitting habit, alternating with silty, thin to medium, calcareous shale beds; sharp, planar contacts between beds; echinoid ossicles, disarticulated and few broken brachiopods, ostracodes(?), gastropods; fossils randomly oriented and distributed; moderate petroliferous odor; very subdued ledge-former ...... 8 25 COVER: Grassy; fossiliferous mudstone float; minor fossiliferous wackestone float...... 13 24 FOSSILIFEROUS MUOSTONE: Dark olive gray (5 V 3/1), weathers to light gray (N7); microcrystalline; medium to thick beds with minor parallel, planar to slightly undulatory, flaggy splitting habit, alternating with silty thin to medium, calcareous shale beds; sharp, planar contacts between beds; echinoid ossicles, disarticulated and few broken brachiopods, gastropods; fossils randomly oriented and 367 distributed; moderate petroliferous odor; very subdued ledge-former ...... 7 23 COVER: Sparsely fossiliferous wackestone, fossiliferous and non-fossiliferous mudstone float ...... 6 22 SPPRSELV FOSS ILIFEROUS WCKESTONE: Grayish black (N3), weathers to medium light gray (N6); microcrystalline; thick beds with very minor, parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with thin to thick, calcareous shale beds; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles, disarticulated and broken brachiopods, gastropods, ostracodes(?); fossils randomly oriented and distributed; fossils in fissile beds subparallel to bedding; weak to moderate petroliferous odor; subdued ledge-former; poorly to moderately well exposed ...... 10 21 COVER: Grassy; non-fossiliferous and fossiliferous mudstone float ...... 14 20 FOSSILIFEROUS MUDSTONE: Dark olive gray (5 Y 3/1), weathers to light olive gray (5 V 6/1); microcrystalline; medium to thick beds with discontinuous, parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with silty, thin to medium, calcareous shale beds; echinoid ossicles and fragments, disarticulated brachiopods; fossils subparallel to bedding to locally randomly oriented, randomly distributed; moderate petroliferous odor; very subdued ledge-former; poorly exposed ...... 6 1.9 COVER: Sparsely fossiliferous wackestone and fossiliferousmudstonefloat ...... 4 18 SPRSELV FOSSILIFEROUS WCKESTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; thick beds with minor parallel, planar to slightly undulatory, flaggy to predominantly slabby splitting habit, alternating with silty, medium to thick, calcareous shale beds; sharp, planar contacts between beds; echinoid ossicles, disarticulated and broken brachiopods, ostracodes, small corals (including indeterminate dissepiraented horn corals); fossils subparallel to bedding, randomly distributed; fissile beds brachiopod-rich (including whole and disarticulated Inflatia cf.I. obsoletus Easton, large Chonetes sp.); moderate petroliferous odor; subdued ledge-former ...... 9 17 COVER: Sparsely fossiliferous wackestone and fossiliferous mudstone float ...... 8 16 SPARSELY FOSSILIFEROUS WACKESTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; slightly silty; thick beds with minor parallel, planar to slightly undulatory, flaggy to predominantly slabby splitting habit, alternating with medium to thick, silty beds with parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar to locally slightly undulatory contacts between beds; echinoid ossicles (wide range of sizes), disarticulated and broken brachiopods, partial trilobites, few broken gastropods(?), ostracodes; most fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; subdued ledge-former ...... 1 COVER: Fossiliferous wackestone and mudstone float ...... 6 14 SPQRSELV FOSSILIFEROUS WCKESTDNEi Dark gray (N3), weathers to light gray (N7); beds with minor parallel, planar to slightly undulatory, flaggy to predominantly slabby splitting habit, alternating with medium to thick, silty beds with parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar to locally slightly undulatory contacts between beds; echinoid ossicles (wide range of sizes), disarticulated and broken brachiopods, partial trilobites, small indeterminate horn corals, few gastropods; most fossils subparallel to bedding, randomly distributed; many additional ostracodes, and whole and disarticulated brachiopods (including indeterminate Product ids, large Chonetes sp. (?))in fissile beds (most fossils parallel to bedding); moderate to strong petroliferous odor; ledge- to subdued 369 1ede-forrner.22 13 FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; thick beds with minor parallel, planar to locally undulatory, slabby splitting habit, alternating with very thin to thin (few medium) beds with parallel, planar to locally undulatory, fissile to laminated splitting habit, sharp, predominantly planar contacts between beds; echinoid ossicles and fragments, few whole and many disarticulated and broken brachiopods, ostracodes('), gastropods; indeterminate, finely comminuted fossil debris; fossils randomly oriented to subparallel to bedding, randomly distributed; faint, thin to medium, planar to locally undulatory lamina locally visible on weathered surface; swirled texture (bioturbat ion) and horizontal burrows common in many thick beds; moderate petroliferous odor; ledge- to subdued ledge-former; moderately well to well exposed; sharp, planar to slightly undulatory contact with unit 12; transition into unit 14 characterized by rapid thickening-upward of fissile/laminated interval ...... 41 CNOTE: Offset 680 feet south along unit 12- unit 13 contact to exposure on small knob at base of east side of Sliderock Mountain, adjacent to and just north of large recent landslide; NW corner of NE 1/4, NW 1/4, NW 1/4, section 25, T.10 9..,R. 4 W.) 12 FOSSILIFEROUS MUDSTONE: Olive black (5 V 211), weathers to medium gray (N5); microcrystalline; slightly silty; medium to thick beds with minor discontinuous, parallel, planar to slightly undulatory, flaggy to slabby splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles, broken pelecypods and brachiopods, ostracodes, few fenestrate bryozoan fragments; fossils parallel to bedding, randomly distributed; faint, slightly disturbed, very thin larnina locally visible on weathered surface; strong petroliferous odor; very subdued ledge-former; poorly exposed ...... a 370 11 COVER: Fossiliferous and non-fossiliferous rnudstone float...... 10 10 FOSSILIFEROUS MUDSTONE: Olive black (5 V 211), weathers to medium gray (N5); microcrystalline; slightly silty; medium to thick beds with minor discontinuous, parallel, planar to slightly undulatory, flaggy to slabby splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles, broken pelecypods(?) and brachiopods; fossils parallel to bedding, randomly distributed; faint, slightly disturbed, very thin lamina locally visible on weathered surface; strong petroliferous odor; poorly exposed...... 5 S COVER: Fossiliferous and non-fossiliferous mudstone float...... 7 8 FOSSILIFEROUS MtjDSTONE: Olive black (5 V 2/1), weathers to very light gray (N8); microcrystalline; thick beds with minor, slightly undulatory to undulatory, flaggy to slabby splitting habit, alternating with medium beds (few thin) with parallel, undulatory, fissile splitting habit; sharp, planar to slightly undulatory contacts between beds; sparsely fossiliferous; echinoid ossicles, disarticulated and broken pelecypods, ostracodes; fossils randomly oriented and distributed; many horizontal to inclined, straight to hooked burrows; moderate petroliferous odor; extensively fractured; very subdued ledge-former; poorly exposed...... 10 7 COVER: Fossiliferous and non-fossiliferous mudstone float...... 4 6 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weather to mediumgray (N5); microcrystalline; slightly silty; medium to thick beds with minor discontinuous, parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with medium beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles, broken brachiopods, ostracodes, few fenestrate bryozoan fragments; fossils parallel to bedding, randomly distributed; faint, slightly undulatory and disturbed, 371 very thin lamina locally visible on weathered surface; strong petroliferous odor; medium/thick beds poorly exposed, fissile/laminated beds very poorly exposed...... 19 S SPRRSELY FOSSILIFEROUS WCKESTONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; thick beds with parallel, planar to slightly undulatory, slabby to blocky splitting habit, alternating with thin to predominantly medium beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; some lateral variations in splitting habit in thick beds; echinoid ossicles, disarticulated and broken brachiopods, ostracodes, few bryozoart(?) fragments; fossils randomly oriented to locally subparallel to bedding, randomly distributed; moderate petrol i ferous odor; ledge-former; gradational contact with unit 6...... 9 4 ECHINOID WCKESTONE: Olive gray (5 V 4/1), weathers to light olive gray (5 V 6/1); microcrystalline; medium to thick beds with very minor parallel, slightly undulatory, slabby splitting habit, alte'nating with thin to medium beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; many echinoid ossicles, disart iculated and broken brachiopods, few fenestrate bryozoan fragments, ostracodes, few partial trilobites, much finely comminuted fossil debris; fossils randomly oriented and distributed; few burrows('); moderate petrol iferous odor; ledge-former; gradational contact with unit S...... 7 3 SPRSELV FOSSILIFEROUS WCKESTONE: Grayish black (N2), weathers to light olive gray (5 V 6/1); microcrystalline; medium to very thick beds (up to 4' thick) with absent to minor parallel, slightly undulatory, slabby splitting habit, alternating with thin to medium beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, disarticulated and 372 broken brachiopods, bryozoan fragments (including indeterminate fenestrates), ostracodes; fossils subpara].lel to bedding, randomly distributed; few scattered, small clusters of fossils in discrete intervals; local swirled texture (=bioturbation); large chert nodules/stringers in upper part (up to 3'long, 1.!' wide); moderate petroliferous odor; ledge-former...... 13 2 FOSSILIFEROUS MUDSIONE: Olive black (5 V 2/1), weathers to medium light gray (N6); microcrystalline; thick to predominantly medium beds very minor, parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with thin to medium beds with parallel to non-parallel, slightly undulatory, fissile to laminated splitting habit; sharp, planar to locally undulatory contacts between beds; echinoid ossicles, disarticulated and broken brachiopods (few whole) and pelecypods, ostracodes, broken gastropods(?); fossils randomly oriented to subparallel to bedding in medium/thick beds, subparallel to parallel to bedding in thin/medium beds, randomly distributed; few short, horizontal burrows; local, slightly swirled texture (bioturbation); extensively fractured in lower part; strong petroliferous odor; ledge-former...... 28 COVER: Talus apron at base of cliffs; fossiliferous mudstone and wackestone, and non-fossiliferous mudstone float ...... uniii. TOTAL: 561.0 feet 373 VIB. SLIDEROC}( MOUNTAIN SECTION_Il NE 1/4, SW 1/4, SW 1/4, SW 1/4, section 24, 1. 10 5., R. 4 W., Spur Mountain quadrangle, U.S.G.S.7,5 minute series. Partial Lombard Limestone section measuredon the eastern end of the north-facing cliffson the northern side of Sliderock Mountain. This section was first described, using Big Snowy Formation nomenclature, by Gealy (1953). This cliff section has a stratigraphically normal-up orientation and is only lacking exposure of the lowermost Lombard. The lower 435 feet of this section crop out in vertical tonear vertical cliffs which cannot be safely measured without the aid ofropes. The following measured section is largely basedon, and concurs with, Gealy's work, although a few minor variationsare noted. Where direct sampling and observation was possible, detailed observationsare included with, or modify, Scaly's observations. Gealy (1953) did not mention where on the cliffs his sectionwas measured. Most of the lower 435 feet of this section (cliffs)was inaccessible to this writer, so modifying and additionalcomments are based on observations and measurements made along theeastern end of the cliffs where a juxtaposed, steep talusslope permits close, although usually indirect observation; "safe"access to the cliffs is possible at a few levels. Scaly's measurements of the uppermost Lombard shalesequence (unit 14), well exposed on an accessibleslope above the cliffs, are too low and seem to have disregarded the covered interval (units 12 and 13) below the shales. Some structural complication involving unit 11 is suggested by the Earlyand Late Mississippian ages provided by corals in theupper part of the unit. The presence of Siphonophylliasp. and Amplexizaphrentis sp. supports a Lombard Limestone interpretation for these rocks, however the presence of Vesiculophyllumsp. suggests that a thrust slice of Madison Limestone, probably LodgepoleLimestone, is also present (Sando, personalcommunication, 1985). The degree of structural complication isunknown. 374 Unit Litholopy Ft. 15 COVER: Grassy; Dark grayish red (10 R 3/2) to dark brownish gray (5 YR 3/1) sandy soil; scattered shale and siltstone to very fine grained sandstone float; basal Amsden Formation...... uflm. 14 SHALE: Olive black (5 V 2/1), weathers to light gray (N7); microcrystalline; silty; very thin to medium beds with parallel, planar to slightly undulatory, fissile to locally laminated splitting habit; non-fossiliferous; very strong petroliferous odor; slope-former...... 35 13 COVER: Grassy; Brownish black (5 YR 2/1) soil; scatteredshalefloat...... 93.3 12 COVER: Grassy; abrupt change to gentle slope; Brownish gray (5 YR 4/1) soil; predominantly fossiliferous wackestone float, minor shale float from above ...... 82 11 FOSSILIFEROUS WACKESTONE/PPCKSTDNE: Olive black (5 V 2/1) to olivegray (5 V 4/1), weathers to yellowish gray (5 V 7/2>; microcrystalline; thick beds with minor parallel, slightly undulatory to locally undulatory, slabby to blocky splitting habit; thin shaly partings between beds; echinoid ossicles and partial stems, disarticulated and broken brachiopods (including Spirifer brazerianus Girty, nthracospirifer curvi lateral is Easton, Pntiauatonia sp., Diaphramus cf. flcestriensis Worthen, Flexaria sp., Inflatia cf. obsoletus Easton, Inflatia sp.., Composita cf. sulcata Weller, and many large, indeterminate Productids; all fossils retrieved from float at base of exposed ledges), bryozoans (including indeterminate fenestrate, Cystoporid, and indeterminate ramose forms), colonial and solitary corals (includingmplexizaphrentis sp., Siphonophyllia sp., Vesiculophvllurasp., indeterminatemplexoid coral), ostracodes, disarticulated and partial trilobites; fossils randomly oriented to locally subparallel to bedding, stand with moderate relief on weathered surface; swirled texture (bioturbation); fossil density very high (packstones) within 375 discrete intervals within some wackestone beds; moderate petroliferous odor; ledge-former...... 18 10 FOSSILIFEROUS WACKESTONE/PfCKSTONE: 01 i ye black (5 V 2/1), weathers to lightgray (N7); microcrystalline; thin to medium beds with minor parallel, planar to slightly undulatory, flaggy splitting habit;very thin to thin shale partings betweenmany beds; slightly silty; echinoid ossicles and fragments, disarticulated brachiopods and pelecypods, ostracodes, few indeterminate bryozoan(?) fragments; fossils subparallel to bedding to locally randomly oriented, randomly distributed; few packstone beds inupper part of unit; moderate petroliferous odor; subdued ledge-former...... 61. 5 9 FOSSILIFEROUS WCKESTONE: Dark olive gray (5 V 3/1), weathers to lightgray (N7); microcrystalline; medium to thick beds (few very thick beds) with minor parallel, slightly undulatory to locally undulatory, flaggy to blocky splitting habit, alternating with thin to locally medium shale beds; sharp, slightly undulatory contacts between beds; echinoid ossicles and partial stems, disarticulated and broken brachiopods, indeterminate corals, partial trilobites, indeterminate bryozoan fragments; fossils randomly oriented to locally subparallel to bedding, randomly distributed; moderate petroliferous odor; ledge-former...... 73. 5 S MUDSTONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; thin to medium beds; slightly undulatory shale partings between beds; non-fossiliferous(1); many elongate chert nodules; subdued ledge-former...... 12 7 MUDSTDNE: Dark gray (N3), weathers to light gray (N7); microcrystalline; slightly silty; thin to thick beds; thin, planar to slightly undulatory shale partings; non-fossiliferous('); few elongate chert nodules and dolomitic limestone bands; ledge-former ...... 65 6 MUDSTONE: Dark gray (N3), weathers to light gray (N7); microcrystalline; slightly 376 silty; thin to medium (few thick) beds with minor parallel, planar to predominantly slightly undulatory, flaggy splitting habit, alternating with very thin to thin beds with parallel, slightly undulatory, laminated to predominantly fissile splitting habit; sharp contacts between beds; non-fossiliferous(?); chert nodules; few thin bands of dolomitic limestone; subdued ledge-former to local ledge-former...... 45.5 S FOSSILIFEROUS MUDSTDNE: Dark olive gray (5 V 3/I), weathers to lightgray (N7); microcrystalline; thin to predominantly medium beds with minor parallel, planar to slightly undulatory, flaggy splitting habit; shale partings; sparsely fossiliferous; few echinoid ossicles, disarticulated and broken brachiopods, indeterminate fossil debris; fossils randomly oriented and distributed; moderate petroliferous odor; ledge-former...... 92 4 MUDSTONE: Dark gray (N3), weathers to medium light gray (N6); microcrystalline; slightly silty; medium to thick beds with minor discontiniious, parallel, slightly undulatory, flaggy to slabby splitting habit, alternating withvery thin to thin shale beds; sharp, slightly undulatory to locally undulatory contacts between beds; non-fossiliferous(?); several elongate chert nodules and stringers; fewvery thin to thin dolornitjc(?) beds; subdued ledge-former to local ledge-former...... 41.5 3 FOSSILIFEROUS MUDSTONE: Dark gray (N3), weathers to medium lightgray (N6); microcrystalline; slightly silty; medium to thick (few thin) beds with minor discontinuous, parallel, planar to slightly undulatory, flaggy to slabby splitting habit, alternating with thin to medium shale beds; sharp, planar to slightly undulatory contacts between beds; few disart iculated and broken brachiopods, echinoid ossieles, ostracodes(?); fossils subparallel to bedding, randomly distributed; moderate to strong petroliferous odor; ledge-former...... 26 2 FOSSILIFEROUS MUDSTONE: Medium dark gray (N4), weathers to medium lightgray (N6); microcrystalline; thick to very thick beds 377 with discontinuous, parallel, planarto slightly undulatory, slabby splitting habit, alternating with very thin to niedium shale beds; sharp, planar to slightly undulatory contacts between beds; sparsely fossiliferous; echinoid ossicles and fragments, ostracodes, broken brachiopods and gastropods(?); fossils subparallel to bedding, randomly distributed; many horizontal burrows; moderate petroliferous odor; ledge-former...... 18 COVER: talus apron at base of Lombard cliff sequence...... unni. TOTAL: 683.5 feet 378 VII. SNCWCREST MOUNTAIN SECTION SE 1/4, NE 1/4, section 1,T. 10 S.., R. 4 W., and SW 1/4, NW 1/4, section 6, 1.10 9.,R. 3 W.., Spur Mountain quadrangle, U.S.G.S. 7.5 minute series. Partial Lombard Limestone sectionmeasured on south-facing cliffsand slope adjacent to the northern arm of an extensive, recent landslide, southwest of Snowcrest Mountain. The section was measured along a south-southwest tonorth-northeast traverse, from the talus field at the baseof the cliffs, to the low relief saddle just northwest of the knob (summit elevation 9,069') in the northwest quarter of section 6. TheLombard is well exposed as near-vertical to vertical cliffs and ledges which impart astairstepappearanceto the cliffs. A few talus-filled chutes located near the eastern end of the cliffs can be utilized for relativelysafe access up the cliffs, although a few short climbs are required. The lowermost Lombard is buried under talus, while the uppermost Lombard is soil- andtalus-covered and/or missing because of erosion. The principal crest of the Snowcrest Range, trending north-south and located just east of the cliffs, is coincident with the hinge lineof the large, east-verging, overturned anticline which characterizes this range. TheLombard Limestone is the oldest unit exposed in the core of the ant iclinein the northern part of the range. The AmsdenFormation is exposed on the overturned, eastern limb of the anticline, very near to the hinge line, suggesting that only a minimal amount of Lombard has been lostby erosion. This raeasured section, therefore, is believed to be relatively complete, with the exception of the missing and/or buried lowermost and uppermost parts of the Lombard, which are believed to be of minimal thickness. The Kibbey is not exposed here, and the Mission Canyon is thrustover the Lombard, abruptly truncating the cliff sequence to the west.. To reach this location, drive south from Alder along Ruby River Road (FR 100) to theLewis Creekjeep road, approximately 0.5 mile northwest of the Vigilante guard station. Hike or drive southwest up this jeep road to thehunterscamp at the end (approximately 2.4 miles). Hike west along the Snowcrest trail, which begins at the southwest end of the camp, to the summit of Snowcrest Mountain. Turn southwest, and hike approximately 0.8 mile to the east end of the northernarm of the large landslide. The easiest approach to the baseof thecliffs is from the east-southeast side of the easternmost end of the landslidearm. 379 Unit Lithology Ft. 72 COVER: Grassy slope; some fossiliferous and non-fossiliferous mudstone float, and minor sparsely fossiliferous wackestone float; medium brownish gray (5 YR 5/1) to brownish cray (5 YR 4/1) soil ...... 228 71 SPARSELY FOSSILIFEROUS WACKESTONE: Dark brownish gray (5 YR 3/1), weathers to light brownish gray (5 YR 6/1); microcrystalline; slightly dolomitic(?); poorly exposed; medium to thick beds, alternating with thin beds with parallel, undulatory, laminated splitting habit; disarticulated and broken brachiopods, echinoid ossicles and fragments, gastropods; fossils randomly oriented and distributed; moderate petroliferous odor; very subdued ledge-former (negligible relief)...... 7 70 CDVER/SPRSELY FOSSILIFEROUS WCKESTONE: Grassy slope; abundant, small sparsely fossiliferous wackestone, and fossiliferous and non-fossiliferous mudstone float; few small, scattered outcrops of sparsely fossiliferous wackestone; outcrops have negligible relief, contain echinoid ossicles and fragments, disarticulated and broken brachiopods, gastropods, ostracodes(?); few outcrops with slightly undulatory to undulatory, flaggy to slabby splitting habit; most outcrops massive, slightly dolomitic(?)...... 37 69 SPARSELY FOSSILIFEROUS WCKESTONE: Olive gray (5 V 4/1), weathers to light brownish gray (5 YR 6/1); microcrystalline; thick beds with very minor, parallel, slightly undulatory to undulatory, slabby splitting habit, alternating with thin to medium beds with parallel, undulatory, laminatedto fissile splitting habit; sharp, undulatory contacts between beds; echinoid ossicles, and fragments, disarticulated brachiopods, few gastropods; fossils randomlyoriented and distributed; moderate petroliferous odor; ledge-former...... S 68 FOSSILIFEROUS WCKESTONE: Olive gray (5 V 4/1), weathers to light brownish gray (5 YR 6/1); microcrystalline; slightly dolornitic(?); very thick bed with discontinuous, parallel, undulatory, slabby splitting habit, between two medium beds with parallel, slightly undulatory, laminated splitting habit; sharp, slightly undulatory contacts between beds; disarticulated and broken brachiopods, echinoid ossicles, few bryozoan(?) fragments; fossils randomly oriented and distributed; moderate petroliferous odor; ledge-former; sharp, undulatory contact with unit 69..... 4 67 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray ( V 4/1), weathers to light gray (N7); microcrystalline; thick beds with minor, discontinuous, parallel, undulatory, flaggy splitting habit, alternating with thin to predominantly medium calcareous shale beds; sharp, slightly undulatory contacts between beds; disarticulated and broken brachiopods (few whole), echinoid ossicles, ostracodes, bryozoan(?) fragments; moderate petroliferous odor; ledge-former; sharp, undulatorycontactwithunit68...... 9 66 FOSSILIFEROUS WACKESTONE: Olive gray (Z V 4/1), weathers to lightgray (N7); microcrystalline; thick beds with minor, discontinuous, parallel, undulatory, flaggy splitting habit, alternating with thin, calcareous shale beds; sharp, slightly undulatory contacts. between beds; whole and disarticulated and few broken brachiopods, echinoid ossicles, ostracodes C?), few bryozoanC?) fragments; fossils randomly oriented and distributed; weak petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit 67...... 6 SPARSELY FOSSILIFEROUS WACKESTDNE: Olive gray ( V 4/1), weathers to light gray (N7); microcrystalline; slightly silty; slightly dolomitic(?); medium to thick beds withrare parallel, slightly undulatory, flaggy splitting habit, alternating with thin beds with parallel, slightly undulatory to locally planar, laminated to fissile splitting habit; echinoid ossicles and few fragments, disarticulated brachiopods, ostracodes; fossils randomly oriented arid distributed, locally subparallel to bedding; strong petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit 66...... 8 381 64 SPRSELV FOSSILIFEROUS WCKESTONE: Olive gray (5 V 4/1), weathers to medium lightgray (N6); microcrystalline; slightly silty; slightly dolomitic(?); very thick to predominantly thick beds with minor parallel, slightly undulatory to undulatory, slabby splitting habit, alternating with thin to (few) medium beds with parallel, undulatory, laminated to locally fissile splitting habit; sharp, undulatory contacts between beds; echinoid ossicles and fragments, whole and disarticulated brachiopods, gastropods, ostracodes(?); fossils randomly oriented and distributed; moderate to strong petroliferous odor; ledge-former; sharp, undulatory contact with unit 65...... 11 63 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to medium lightgray (N6); microcrystalline;very thick bed with parallel, slightly undulatory to undulatory, slabby splitting habit; few echinoid ossicles, disarticulated brachiopods; fossils subparallel to bedding, randomly distributed; strong petroliferous odor; very subdued ledge-former; sharp, undulatory contact with unit 64...... * ...... 3 62 SPfRSELY FOSSILIFEROUS WCKESTONE: Dark olive gray (5 V 3/1), weathers to medium light gray (N6); microcrystalline; slightly silty; three thick beds, alternating with thin calcareous shale beds; sharp, slightly undulatory contacts between beds; echinoid ossicles and fragments, broken and few disarticulated braciopods; fossils subparallel to bedding, randomly distributed; strong petroliferous odor; very subdued ledge-former; sharp, planar contact with unit 63...... 4 61 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to mediumlight gray (N6); microcrystalline; slightlysilty; very thick(?) bed with parallel, undulatory, laminated to locally fissile splitting habit; few disarticulated brachiopods,few echinoid ossicles; fossils subparallelto parallel to bedding, randomly distributed; very strong petroliferous odor; subdued ledge-former; sharp, slightly undulatory contact with unit 62...... 4 382 60 SPRSELV FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/I), weathers to lightgray (N7); microcrystalline; slightly silty; slightly dolomitic; thick tovery thick (one 4' thick) beds withrare parallel, slightly undulatory, slabby splitting habit, alternating with thin beds with parallel, undulatory, laminated to fissile splitting habit; sharp, undulatory contacts between beds; echinoid ossicles, whole and disarticulated brachiopods, gastropods, ostracodes; fossils randomly oriented and distributed, brachiopods in all beds; few random burrows(?);strong petroliferous odor; ledge-former...... 9.5 59 FOSSILIFEROUS WPCKESTONE: Olive gray (5 V 4/1), weathers to lightgray (N7); microcrystalline; two thick beds with very minor, discontinuous, parallel, undulatory, slabby splitting habit, alternating with thin and medium beds with parallel, undulatory, laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, whole and disarticulated brachiopods, few bryozoanC?) fragments, few gastropods; fossils randomlyoriented and distributed, slight lateralvariation in fossil density; brachiopods inall beds; moderate petroliferous odor; ledge-former; sharp, slightly undulatory contactwith unit 60...... 6 58 SPRSELV FOSSILIFEROUS WACKESTONE: Dark Olive gray (S V 3/1), weathers tomedium light gray (N6); microcrystalline;slightly silty; slightly dolomitic; thickbeds, alternating with thin beds with parallel, slightly undulatory, laminated tofissile splitting habit; sharp, undulatorycontacts between beds; disarticulated brachiopods, echinoid ossicles; fossils randomly oriented and distributed; moderate petroliferous odor; ledge-former;sharp, undulatory contact with unit 59...... 5 57 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to yellowishgray (5 V 8/1); microcrystalline;medium to thick beds with minor, parallel,slightly undulatory, slabby splitting habit, alternating with thin to predominantly medium beds with parallel, slightly 383 undulatory, laminated to fissile splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles and fragments, few disarticulated and broken brachiopods, few partial trilobite molds, disarticulated pelecypods(?), few small fenestrate bryozoan fronds; slightly swirled texture (= bioturbation); fossils subparallel to bedding and distributed; several small chert nodules; strong petroliferous odor; ledge-former; sharp, undulatorycontact with unit 58...... 7 56 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to yellowishgray (5 V 8/1); microcrystalline; thickbeds with minor, parallel, slightly undulatory, slabby splitting habit, alternating with medium beds with parallel, planar to predominantly slightly undulatory, laminated splitting habit; sharp, undulatory contacts between beds; echinoid ossicles and fragments, variably sized whole and disarticulated brachiopods, disarticulated and partial trilobites, ostracodes; fossils randomly oriented and distributed; few chert nodules; strong petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit 57...... 14 55 FOSSILIFEROUS MUDSTONE: Dark olive gray (5 V 3/1), weathers to medium brownish gray (5 YR 5/1); microcrystalline; slightly silty; slightly dolomitic; medium to thick beds withvery minor, parallel, planar to slightly undulatory, flaggy splitting habit, alternating with medium beds with parallel, undulatory, laminated to fissile splitting habit; sharp, planar to slightly undulatory contacts between beds; sparsely fossiliferous; echinoid ossicles, disarticulated and broken brachiopods and few pelecypods(?), gastropods; fossils randomly oriented and distributed;many randomly oriented burrows; moderate petroliferous odor; ledge- to subdued ledge-former; sharp, slightly undulatory contact with unit 54...... 54 FOSSILFEROUS MUDSTDNE: Dark olive gray (5 Y 3/1), weathers to mediumbrownish gray (5 YR 5/1); microcrystalline; slightly silty; medium beds alternating 384 with medium beds with parallel,slightly undulatory, laminated to fissile splitting habit; sharp, slightly undulatorycontacts between beds; sparsely fossiliferous; echinoid ossicles, disarticulated brachiopods; fossils subparallel to bedding, randomly oriented; strong petroliferous odor; subdued ledge-former;sharp, slightly undulatory contact with unit 55 ...... 6 33 FOSSILIFEROUS MUDSIONE: Dark olive gray (3 V 3/i), weathers to yellowishgray (5 V 8/I); microcrystalline;silty to (fine) sandy; thick beds with minor parallel, slightly undulatory, slabbyto locally flaggy splitting habit, alternating with medium beds with parallel, undulatory, laminated to locally fissile splitting habit; sharp, slightlyundulatory contacts between beds; echinoid ossicles and fragments, disarticulated andbroken brachiopods and few pelecypods, few bryozoanC?) fragments, ostracodes, gastropods; fossils randomly orientedand distributed; moderate petroliferousodor; ledge- to subdued ledge-former;sharp, planarcontactwithunit54...... 15 32 FOSSILIFEROUS MUDSTONE: Grayish black (N2) to black (Ni), weathers to yellowishgray (5 V 8/1); microcrystalline;silty; medium to (few) thick beds with parallel,slightly undulatory to predominantly planar,flaggy splitting habit, alternating with thickto (few) very thick, calcareous shalebeds; sharp, planar to slightly undulatory contacts between beds; sparsely fossiliferous; broken echinoid ossicles, disarticulated and broken brachiopods (including Inflatia sp., Sirifersp. (possibly brazerianus Girty), ntiguatonia? sp.), ostracodes, gastropods; fossils subparallel to bedding tolocally randomly oriented, randomly distributed; small, horizontal to slightlyinclined, straight to hooked burrows; strongto very strong petroliferous odor; medium/thick beds form ledges, shales poorlyexposed (slope-former)...... 14 51 SPARSELY FOSSILIFEROUS WCKESTONE: Dark olive gray (5 V 3/1), weathersto light gray (N7); microcrystalline; silty; medium beds with parallel, planarto 385 undulatory, flaggy splitting habit, alternating with thick, calcareous shale beds; sharp, planar contacts between beds; many echinoid ossicles and fragments, whole and disarticulated brachiopods (including indeterminate Product ids, possibly Inflatia sp.'), ostracodes, gastropods Cup to 1" long); fossils randomly oriented in flaggy beds, subparallel to bedding in shale beds, randomly distributed; strong tovery strong petroliferous odor; medium beds form ledges, shales poorly exposed (slope-former)...... S 50 SPARSELY FOSSILIFEROUS WCKESTONE: Olive gray C! V 4/1), weathers to medium gray (N!); microcrystalline; medium to thick beds with very minor, parallel, slightly undulatory, slabby splitting habit, alternating with thin to medium, calcareous shale beds; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and many fragments, bryozoari fragments, small whole pelecypods, few small disarticulated brachiopods, gastropods; fossils subparallel to bedding, randomly distributed; local swirled texture (bioturbation); strong petrol i ferous odor; ledge-former; contact with unit 51 obscurred by talus...... 9 49 FOSSILIFEROUS MUDSTONE: Dark olive gray (5 V 3/1), weathers to medium lightgray (N8); microcrystalline; medium to thickbeds with minor parallel, planar to slightly undulatory, flaggy splitting habit, alternating with medium to predominantly thin beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; sparsely fossiliferous; echinoid ossicles, disarticulated brachiopods and few pelecypods(?), rare gastropod; fossils randomly oriented and distributed; strong petrol i ferous odor; subdued ledge-former; sharp, slightly undulatory contact with unit 50...... 5 48 SPQRSELV FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to mediumgray (N!) to grayish orange (10 YR 7/4); microcrystalline; medium to predominantly thick beds with minor, parallel, slightly undulatory, slabby splitting habit, alternating with thin, calcareous shale beds; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, few whole andmany disarticulated pelecypods, clisarticulated brachiopods, few bryozoan fragments, ostracodes, few gastropods; fossils subparallel to bedding, randomly distributed, some silicified; few stylolites, few randomly oriented burrows; strong petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit 49...... 13 47 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray CZ V 4/1), weathers to medium gray to grayish orange (10 YR 7/4); microcrystalline; medium to thick beds with very minor, parallel, slightly undulatory, slabby splitting habit, alternating with thin to medium, calcareous shale beds; sharp, planar to slightly undulatory contacts betweeen beds; echinoid ossicles and fragments, whole. and disarticu].ated pelecypods, disart iculated brachiopods, gastropods, few bryozoan fragments; most fossils subparallel to parallel to bedding, randomly distributed; local swirled texture (=bioturbation); few randomly oriented burrows; strong petroliferous odor; ledge-former; sharp, slightly undulatorycontact with unit 48...... 7 48 FOSSILIFEROUS MUDSTONE: Olive gray ( Y 4/1), weathers to lightgray (N7); microcrystalline; medium to thick beds with minor parallil, slightly undulatory to locally undulatory, slabby splitting habit, alternating with medium to predominantly thin, calcareous shalebeds; sharp, slightly undulatory contactsbetween beds; few echinoid ossicles,disarticulated brachiopods and (few) pelecypods, ostracodes(?); fossils randomly orientedto locally subparallel to bedding,randomly ditributed; few horizontal to inclined burrows; few stylolites; strong petrol iferous odor; ledge-former;contact with unit 47 obscurred by talus...... 16 45 SPRSELV FOSSILIFEROUS WCKESTONE Medium olive gray (5 V5/i),weathers to light gray(N7);microcrustalline; medium to thick beds with rare, parallel, slightly undulatory splitting habit, alternating with medium beds with parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar contacts between beds; echinoid ossicles and fragments, ostracodes, few gastropods, disart iculated and few whole brachiopods, few disarticulated pelecypods; fossils randomly oriented and distributed; few, horizontal to slightly inclined, dendroid burrows (1/20" diameter); few stylolites; strong petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit 46...... 8 44 FOSSILIFEROUS MUDSTDNE: Olivegray (5 V 4/I), weathers to yellowish gray (5 V 8/1); raicrocrystaliine; medium beds withrare parallel, slightly undulatory, flaggy splitting habit, altrenating with medium to predominantly thin, calcareous shale beds; sharp, planar to slightly undulatory contacts between beds; ostracodes, echinoid ossicles, few (sparry calcite-filled) whole and disart iculated brachiopods, broken gastropods(); fossils randomly oriented and distributed; few horizontal to inclined burrows; strong petroliferous odor; ledge-former; sharp, planar contact with unit45...... 10 43 SPARSELY FOSSILIFEROUS WCKESTONE: Olive gray (5 V 4/1),weathers to light gray (N7); microcrystalline; medium to thick beds with minor, discontinuous, parallel, slightly undulatory, flaggy to slabby splitting habit, alternating with medium to predominantly thin beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, disarticulated and (few) whole brachiopods (few with geopetal fill), few disarticulated pelecypods, ostracodes, gastropods; fossils randomly oriented and distributed; moderate petrol iferous odor; ledge-former; corit act with unit 44 obscurred by talus...... 42 FOSSILIFEROUS MUDSTONE: Olive gray (5 Y 4/1), weathers to mdeiurn lightgray (N6); microcrystalline; thick to predominantly medium beds with rare parallel, slightly undulatory, flaggy splitting habit, alternating with medium to predominantly thin beds with parallel, planar to slightly undulatory, fissila to laminated splitting habit; sharp, slightly undulatory contacts between beds; whole and disariculated brachiopods (many Productids), echinoid ossicles, few gastropods; fossils randomly oriented and distributed; few randomly oriented burrows; few stylolites; strong petroliferous odor; subdued ledge-former; sharp, slightly undulatorycontactwithunit43...... 11 41 FOSSILIFEROUS 2RINSTDNE: Light olive gray (5 V 6/1) to very pale yellowish brown (10 YR 7/2), weathers to pale grayish orange (10 YR 8/4); microcrystalline; slightly dolomitic; very thick, massive beds; very indurate; many echinoid ossicles and few partial stems,many fenestrate and indeterminate bryozoan fragments, disarticulated and broken brachiopods, few gastropods, ostracodes; fossils randomly oriented and distributed; very weak petroliferous odor; cliff-former; sharp, planar contact with unit 42...... 31 40 MUDSIONE: Dark brownish gray (5 YR 3/1), weathers to medium light gray (N6); microcrystalline; medium to thick beds with rare parallel, planar to slightly undulatory, flaggy splitting habit, alternating with medium beds with parallel, planar to slightly undulatory, laminated to fissile splitting habit; sharp, planar to slightly undulatory contacts between beds; strong petroliferous odor;very subdued lodge-former; sharp, planar contact with unit 41...... 6 39 SPRSELV FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to light gray (N7); microcrystalline; thick bed between two medium, silty, calcareous shale beds; sharp, planar contacts between beds; echinoid ossicles, disarticulated and broken brachiopods, gastropods; fossils randomly oriented and distributed; weak petrol i ferous odor; led ge-former; sharp, slightly undulatory contact with unit 4'...... 3 38 FOSSILIFEROUS MUDSTONE: Dark brownish gray (5 YR 3/1), weathers to medium lightgray (N6); microcrystalline; slightly silty; medium beds alternating with thin to medium beds with parallel, planar, laminated to fissi].e splitting habit; sharp, planar contacts between beds; sparsely fossiliferous; echinoid ossicles, small disarticulated and broken brachiopods; fossils subparallel to bedding, randomly distributed; moderate petroliferous odor; ledge-former; sharp, planarcontactwithunit39...... *4 37 MUDSTDNE: Brownish black (5 YR 2/1), weathers to light gray (N8); microcrystalline; slightly silty; medium to thick beds with rare parallel, slightly undulatory, flaggy splitting habit, alternating with medium beds with parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar contacts between beds; strong petroliferous odor; subdued ledge-former; sharp, slightly undulatorycontactwithunit38...... 7 38 FOSSILIFEROUS MUDSTONE: Dark brownish gray (5 YR 3/1), weathers to medium lightgray (N6); microcrystalline; slightly silty; thick beds with minor, parallel, planar to predominantly slightly undulatory, slabby to locally flaggy splitting habit, alternating with medium to (few) thin beds with parallel to non-parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, small disarticulated and broken brachiopods, ostracodes('); fossils randomly oriented and distributed; few horizontal to inclined burrows(?); moderate petroliferous odor; ledge-former; sharp, planarcontactwithunit37...... 12 35 MUDSTONE: Brownish black (5 YR 3/1), weathers to medium lightgray (N6); microcrystalline; slightly silty; medium beds with rare discontinuous, parallel, planar flaggy splitting habit, alternating with thin to medium beds with parallel, I!J planar to slightly undulatory, laminatedto predominantly fissile splitting habit; sharp, planar to locally slightly undulatory contacts between beds; strong petrol i ferous odor; subduedledge-former; sharp, planar contact with unit 36...... 8 34 SPARSELY FOSSILIFEROUS WACIcESTONE:Olive gray (5 V 4/1), weathers to yellowish gray (5 Y 8/1); microcrystalline; slightly silty; thick beds with minor parallel, planar to slightly undulatory, slabby splitting habit, alternating with medium beds with parallel, undulatory, fissileto laminated splitting habit; sharp, planar contacts between beds; echinoid ossicles, disarticulated brachiopods, few broken and disarticulated pelecypods(?); fossils randomly oriented and distributed; moderate petrol i ferous odor; ledge-former; contact with unit 35 obscurred bytalus...... 7 33 FOSSILIFEROUS MUDSTONE: Dark brownish gray (5 YR 3/1), weathers to raediwalight gray (N6); microcrystalline; slightlysilty; medium to thick beds with minorparallel, planar to slightly undulatory,flaggy to slabby splitting habit, alternatingwith thin to predominantly mediumbeds with parallel, planar to undulatory, fissile to laminated splitting habit;sharp, planar contacts between beds; sparsely fossiliferous; echinoid ossicles, ostracodes, broken brachiopods; fossils subparallel to bedding, randomly distributed; small, grayish black (N2) wisps parallel to bedding; fewhorizontal burrows; strong petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit 34...... 9 32 MUDSTONE: Brownish black (5 YR 2/I), weathers to medium lightgray (N6); microcrystalline; thick to very thick beds with rare, parallel,slightly undulatory, blocky splitting habit, alternating with thin to medium beds with parallel, planar to slightly undulatory, fissile to laminatedsplitting habit; sharp, planar to slightly undulatory contacts between beds; thick/very thick bedsare laminated chert-limestones (chert layers 1U to2" thick, grayish orange (10 YR 7/4), interbedded with 4" to 8" thick mudstones, has striped appearance); strong petroliferous odor; cliff-former; fissile/laminated intervals less resistant; sharp slightly undulatory contact with unit 33 ...... 31 FOSSILIFEROUS MUDSTONE: Brownish black ( YR 2/1), weathers to light gray (N7); microcrystalline; slightly silty; thick beds with minor parallel, planar, slabby splitting habit, alternating with medium beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, planar contacts between beds; sparsely fossiliferous; echinoid ossicles, ostracodes(?), disarticulated small brachiopods and/or pelecypods(?); fossils subparallel to bedding; few small, black (Ni) wisps parallel to bedding; strong petroliferous odor; subdued ledge-former; sharp, planar contact with unit 32...... 30 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray ( V 4/1), weathers to light gray (N7); microcrystalline; medium beds alternating with medium to thick beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, planar contacts between beds; echinoid ossicles, disarticulated and broken brachiopods and (few) pelecypods; fossils randomly oriented and distributed; moderate petrol iferous odor; ledge-former; sharp, slightly undulatory contact with unit 31...... 29 FOSSILIFEROUS MUDSTONE: Light olive gray (Z V 6/i), weathers to light gray (N7); microcrystalline; thick beds with rare parallel, planar to slightly undulatory, slabby splitting habit, alternating with medium to thick beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, planar contacts between beds; many echinoid ossicles, many disarticulated and broken brachiopods, few disarticulated pelecypods, few fenestrate bryozoari fragments; fossils randomly oriented and distributed; moderate petroliferous odor; cliff-former; sharp, planarcontact with unit 30 ...... 7 28 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray (5 V 411), weathers to light gray (N7); microcrystalline; medium to predominantly thick beds with rare, parallel, planar to slightly undulatory, flaggy to slabby splitting habit; sharp, planar to locally slightly undulatory contacts between beds; echinoid ossicles and fragments, disarticulatad and broken brachiopods and few pelecypods('), few gastropods; fossils randomly oriented and distributed; moderate petroliferous odor; ledge- to subdued ledge-former; sharp, slightly undulatory contact with unit 29...... ii 27 FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to light gray (N7); microcrystalline; medium to predominantly thick beds with rare parallel, slightly undulatory, slabby splitting habit, alternating with medium and few thick beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, planar contacts between beds; many disarticulated and broken brachiopods, echinoid ossicles, gastropods, few fenestrate(?) bryozoan fragments, ostracodes('); fossils randomly oriented and distributed; few horizontal to slightly inclined burrows; moderate petrol iferous odor; ledge-former; sharp, slightly undulatorycontactwithunit28 ...... 8 26 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray (5 V 5/1), weathers to medium light gray (N6); microcrysatlline; medium to thick beds with minor parallel, slightly undulatory, slabby splitting habit, alternating with medium to (few) thick beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, planar contacts between beds; echinoid ossicles and fragments, broken and disarticulated brachiopods, gastropods; fossils randomly oriented and distributed; moderate petrol iferous odor; ledge-former; sharp, planar contact with unit 27...... 7 25 FOSSILIFEROUS WACKESTONE: Light olive gray (5 V 5/1), weathers to light gray (N7); microcrystalline; thick beds with very minor parallel, planar to slightly undulatory, slabby splitting habit, alternating with medium to thick beds with parallel, planar, fissile to predominantly laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; many echinoid ossicles, disarticulated and few broken brachiopods and few pelecypods, few fenestrate bryozoan fragments, ostracodes(?), few partial trilobite molds, gastropods; fossils randomly oriented and distributed; local swirled texture (bioturbation); few burrows(?); moderate petroliferous odor; ledge-former; sharp, planarcontactwithunit26 ...... 12 24 SPARSELY FOSSILIFEROUS WACKESTONE: Medium olive gray (5 V 5/1), weathers to medium light gray (N6); microcrystalline; medium to thick beds with minor parallel, slightly undulatory, slabby splitting habit, alternating with medium to thick beds with parallel, planar to slightly undulatory, fissile to laminated splitting habit; sharp, slightly undulatory to predominantly planar contacts between beds; echinoid ossicles and fragments, disarticulated and few broken brachiopods, few gastropods; most fossils subparallel to bedding, locally randomly oriented, randomly distributed; moderate petrol iferous odor; ledge-former; sharp, planar contact with unit 25...... 9 23 FOSSILIFEROUS WACKESTONE: Light olive gray (5 V 6/i), weathers to light gray (N7); microcrystalline; thick beds with very minor, parallel, planar to slightly undulatory, slabby splitting habit, altern4ting with medium to thick beds with parallel, planar, fissile to predominantly laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; echinoid ossicles and fragments, disarticulated and broken brachiopods and pelecypods, gastropods, ostracodes, disarticulated trilobites, few fenestrate bryozoan fragments; fossils randomly oriented and distributed; swirled texture (=bioturbation); fGw horizontal burrows; moderate petroliferous odor; cliff-former; sharp, planar contact with unit 24...... 11 22 SPARSELY FOSSILIFEROUS WACKESTONE: Light olive gray (5 V 6/1), weathers to light gray (N7); microcrystalline; medium and thick beds alternating with medium beds with parallel, planar, fissile to laminated splitting habit; sharp, planar contacts between beds; echinoid ossicles, broken and disarticulated brachiopods; fossils randomly oriented and distributed; moderate petrol iferous odor; ledge-former; sharp, planar contact with unit 23...... 4 21 FOSSILIFEROUS MUDSTONE: Dark olive gray (5 V 3/1), weathers to light gray (N7); microcrystalline; mediura to thick beds with rare parallel, slightly undulatory, slabby splitting habit, alternating with thin to medium beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, planar contacts between beds; sparsely fossiliferous; echinoid ossicles, few disarticulated and broken brachiopods; fossils randomly oriented and distributed; strong petroliferous odor; subdued ledge-former; sharp, slightly undulatory contact with unit 22 ...... B 20 SPARSELY FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to light gray; microcrystalline; medium to thick beds with rare parallel, slightly undulatory, slabby splittirg habit, alternating with thin beds with parallel, planar, laminated to predominantly fissile splitting habit; sharp, planar contacts between beds; echinoid ossicles, gastropods, few broken and disarticulated brachiopods; fossils randomly oriented and distributed; moderate petrol iferous odor; ledge-former; sharp, planar contact with unit 21...... 6 19 FOSSILIFEROUS MUDSTDNE: Dark olive gray (5 V 3/1), weathers to medium light gray (N6); microcrystalline; medium to thick beds alternating with medium to (few) thin beds with parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar contacts between beds; echinoid ossicles, disarticulated and few broken brachiopods, ostracodes(?), few gastropods; fossils subparallel to bedding, locally randomly oriented, randomly distributed; strong petroliferous odor; subdued ledge-former; sharp, planar contact with unit 20...... ii 18 FOSSILIFEROUS MUDSTONE: Dark olive gray (5 V 3/1), weathers to medium light gray (N6); microcrystalline; medium beds alternating with thin to (few) medium beds with parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar contacts between beds; few echinoid ossicles and fragments, disarticulated and broken brachiopods; fossils subparallel to bedding, randomly distributed; strong petrol iferous odor; subdued ledge-former; sharp, planarcontactwithunitl9...... 8 17 SPPRSELV FOSSILIFEROUS WCKESTONE: Olive gray (5 V 3/1), weathers to medium light gray (N6) to light gray (N7); microcrystalline; thin to predominantly medium beds with rare parallel, slightly undulatory, flaggy splitting habit, alternating with thin to (few) medium beds with parallel, slightly undulatory, laminated to predominantly fissile splitting habit; sharp, slightly undulatory contacts between beds; predominantly echinoid ossicles, few disarticulated and broken brachiopods, gastropods; fossi is randomly oriented and distributed; moderate petroliferous odor; ledge-former; sharp, planar bontact with unit 18...... 12 16 FOSSILIFEROUS MUDSIONE: Dark olive gray (5 V 3/1), weathers to light gray (N7); microcrystalline; thin to medium beds, alternating with thin to medium beds with parallel, planar to predominantly slightly undulatory, fissile to laminated splitting habit; sharp, planar to locally slightly undulatory contacts between beds; echinoid ossicies, disarticulated and broken brachiopods, ostracodes(?), few gastropods; fossils subparallel to bedding, locally randomly oriented, randomly distributed; moderate petroliferous odor; subdued ledge-former; sharp, planar contact with unit 17...... 8 15 SPARSELY FOSSILIFEROUS WACKESTONE: Medium dark gray (N4), weathers to medium light gray (N6); microcrystalline; slightly silty; thin to medium beds alternating with medium to predominantly thin beds with parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar contacts between beds; echinoid ossicles, few disarticulated and broken brachiopods; fossils randomly oriented and distributed; strong petroliferous odor; subdued ledge-former; sharp, planar contact with unit 16...... 6 14 FOSSILIFEROUS WACKESTDNE: Olive gray (5 V 4/1), weathers to light olive gray (5 V 6/1); microcrystalline; slightly silty; medium to thick beds with minor parallel, slightly undulatory, slabby splitting habit, alternating with thin to medium beds with parallel, planar to slightly undulatory, laminated to predominantly fissile splitting habit; sharp, planar contacts between beds; faint, thin, planar lamina locally visible on weathered surface; few whole and disarticulated brachiopods, echinoid ossicles, gastropods; fossils subparallel to bedding, randomly distributed, stand with slight relief on weathered surface; few chert nodules; moderate petroliferous odor; ledge-former; sharp, planar contact with unit 15...... 10 13 SPARSELY FOSSILIFEROUS WACKESTONE: Medium dark gray (N4), weathers to light olive gray (5 V 6/1); microcrystalline; medium to (few) thin beds with rare parallel, planar to lightly undulatory, flaggy to slabby splitting habit, alternating with thin to medium beds with parallel, slightly undulatory, laminated to predominantly fissile splitting habit; sharp, slightly undulatory to predominantly planar contacts between beds; echinoid ossicles, few disarticulated and broken brachiopods, ostracodes('); fossils randomly oriented and distributed; strong petrol i ferous odor; subdued ledge-former; sharp, planar contact with unit 14...... 7 12 FOSSILIFEROUS WACKESTONE: Olive gray (5 V 4/1), weathers to light olive gray (5 V 6/i.) to pale yellowish brown (10 YR 6/2); microcrystalline; slightly silty.; thin to medium beds with rare, parallel, planar to slightly undulatory, flaggy splitting habit, alternating with thin beds with parallel, planar to undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; thin, planar to slightly undulatory lamina locally visible on weathered surface; many echinoid ossicles,(few) whole and disarticulated brachiopods, gastropods; fossils randomly oriented and distributed, stand with slight relief; several chart nodules and stringers (up to 4" wide, 15'lonq); few small, dark brownish gray (5 YR 3/1) wisps parallel to bedding; moderate to strong petroliferous odor; subdued ledge-former; sharp, planar contactwithunitl3 ...... IS 11 FOSSILIFEROUS MUDSTDNE: Olive black (5 V 2/1), weathers to light gray (N7); microcrystalline; medium to thick beds with minor parallel, slightly undulatory, flaggy splitting habit, alternating with thin to (few) medium beds with parallel, undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; sparsely fossiliferous; disarticulated and broken brachiopods, echinoid ossicles, few gastropods; fossils subparallel to bedding, randomly distributed; strong petroliferous odor; subdued ledge-former; sharp, slightly undulatorycontact with unit 12...... 7 10 FOSSILIFEROUS WCKESTONE/MUDSTONE: Dark gray (N3), weathers to light gray (N6); microcrystalline; medium to predominantly thick beds ((2' thick) with minor parallel, planar to slightly undulatory, slabby to locally slabby splitting habit, alternating with thin beds with parallel, slighlty undulatory, fissile to predominantly laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; many echinoid ossicles (several broken), disarticulated and broken brachiopods and pelecypods(?), gastropods, bryozoan(?) fragments; fosi ls randomly oriented and distributed, locally subparallel to bedding; few intermittent less fossiliferous beds (=fossi 1 iferous mudstones); moderate to strong petrol i ferous odor; ledge-former; sharp, planar contact with unit 11...... 13 9 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to lightgray (N7) to pale grayish orange (10 YR 314); microcrystalline; medium to thick beds with minor parallel, planar to slightly undulatory, flaggy to slabby splitting habit, alternating with thin to medium beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; faint, slightly undulatory, thin lamina locally visible on weathered surface; sparsely fossiliferous; echinoid ossicles, disarticulated and broken brachiopods; fossils subparallel to bedding, randomly distributed; scarce chert nodules; strong petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit 10...... S 8 FOSSILIFEROUS WPCKESTONE: Dark brownish gray (5 V 3/1), weathers to medium light gray (N6); microcrystalline; thick to predominantly medium beds with minor parallel, planar to slightly undulatory, flaggy splitting habit, alternating with thin to medium beds with parallel, slightly undulatory, fissile to laminated splitting habit; sharp, planar to slightly undulatory contacts between beds; many echinoid ossicles and fragments, few bryozoan fragments, disart iculated brachiopods, gastropods; fossils parallel to bedding, randomly distributed, slightly less fossilferous than unit 5; moderate petroliferous odor; ledge-former; sharp, planar contact with unit 9...... 9 7 FOSSILIFEROUS MUDSTDNE: Olive black (5 V 4/1), weathers to light gray (N7) to pale grayish orange (10 YR 8/4); microcrystalline; medium to predominantly thick beds with minor parallel, slightly undulatory to undulatory, flaggy to slabby splitting habit, alternating with thin beds with parallel, undulatory, fissile to laminated splitting habit; sharp, undulatory contacts between beds; echinoid ossicles, gastropods, few whole and disarticulated brachiopods (few broken), disarticulated pelecypods, ostracodes(?); fossils randomly oriented (smaller fossils typically subparallel to parallel to bedding), randomly distributed; few chart nodules and small stringers; moderately fractured; strong petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit B ...... 14 6 FOSSILIFEROUS MUDSTONE: Brownish black (5 YR 2/1), weathers to medium gray (N5); microcrystalline; thick bed with parallel to locally non-parallel, undulatory, fissile to predominantly laminated splitting habit; sparsely fossiliferous; echinoid ossicles, disarticulatad brachiopods and pelecypods, ostracodes(?); fossils parallel to bedding, randomly distributed; very strong petroliferous odor; slope-former; sharp, slightly undulatorycontactwithuriit7...... 3 S FOSSILIFEROUS WCKESTONE: Dark brownish gray (5 YR 3/1), weathers to light gray (N7); microcrystalline; medium to thick beds with minor parallel, slightly undulatory, slabby splitting habit, alternating with thin to medium beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, disarticulated and broken brachiopods (few whole) and pelecypods; fossils randomly oriented and distributed; most fossils subparallel to bedding, randomly oriented; few small chei't nodules; moderately fractured; strong petrol i ferous odor; ledge-former; sharp, planar contact with unit 6...... S 4 FOSSILIFEROUS MUDSTONE: Olive black (5 V 2/1), weathers to light gray (N7); microcrystalline; medium to thick beds with very minor parallel, undulatory, slabby splitting habit, alternating with thin beds with parallel, slightly undulatory to undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; echinoid ossicles, whole and disarticulated brachiopods, few gastropods; most fossils subparallel to bedding, randomly distributed; few chert nodules'and small stringers; strong petroliferous odor; ledge-former; planar contact with unit S...... 5 3 FOSSILIFEROUS WC}(ESTONE: Dark brownish gray (5 V 3/1), weathers to very pale yellowish brown (10 YR 7/2); microcrystalline; thick beds with minor parallel, slightly undulatory, slabby splitting habit, alternating with thin beds with parallel, undulatory, fissile to laminated splitting 400 habit; sharp, slightly undulatory contacts between beds; many echinoid ossicies arid fragments, bryozoan fragments, few whole and many disarticulated and broken brachiopods, gastropods, ostraccides; fossils parallel to bedding, randomly distributed; few small intraclasts("); moderately fractured; strong petrol iferous odor; ledge-former; sharp slightly undulatorycontactwithunit4...... 6 2 FOSSILIFEROUS MUDSTCNE: Olive black C! V 2/1), weathers to pale grayishorange (10 YR 8/4); microcrystalline; medium to (few) thick beds with minor parallel, slightly undulatory to undulatory, flaggy to slabby splitting habit, alternating with thin to (few) medium beds with parallel, undulatory, fissile to laminated splitting habit; sharp, slightly undulatory contacts between beds; faint, undulatory, thin Iamina visible on weathered surface; sparsely fossiliferous; echinoid ossicles, gastropods, disarticulated and broken brachiopods (few whole) and pelecypods, ostracodes; smaller fossils parallel to bedding, larger fossils randomly oriented, randomly distributed; few small, dark gray (N3) to medium light gray (NS) wisps parallel to bedding; few chert nodules arid stringers; extensively fractured; strong petroliferous odor; ledge-former; sharp, slightly undulatory contact with unit 3...... 11 COVER: talus apron at base of cliffs...... ursm. TOTAL: g74t feet 401 VIII. CLOVER MEADOW SECTION SW 1/4, NE 1/4, section 16,1. 9 S.,R. 2 W.., Varney quadrangle, USGS 15 minute series. Partial Lombard Limestone section measured along a north-south traverse on two sets of south-facing cliffs separated by a gently sloping hummocky interval. The cliffs are present as slip faces created by large-scale slumping and bedding plane failure in the Lombard Limestone. The lower cliffs (units 1-4) surround an amphitheater filled with very large Lombard Limestone talus blocks. The upper cliffs (units 6-It) are separated from the lower cliffs by a grassy, hummocky slope (unit 5) several hundred feet in width. Slumping and sliding has presumably been facilitated by failure and westward transport along gently westward-dipping bedding planes within the Lombard Limestone and/or at, ornear, the Mission Canyon-Lombard Limestone interface. Hadley (1969) had originally mapped these rocks as Mississippian Mission Canyon Limestone and Mississippian- Pennsylvanian Amsden Formation. Several corals retrieved from these rocks indicate a Chesterianage for these rocks (Sando, personal communication, 1985) and theyare here considered of Lombard Limestone affinity. The overlying Amsden Formation, exposed at the top of the upper cliffs, is distinguishable by its red iron-stained color, and poorly to moderately well exposed siltstone, sandstone, and dolomite beds. The base of the red soil and stain maintains a relatively constant stratigraphic position along the upper cliff sequence, although chutes and gullies which traverse this stratigraphic level andpass through the underlying Lombard Limestone are also commonly stained red and/or filled with a reddish soil. The actual base of themsden Formation is characterized by a white, discontinuously exposed ledge of dolomite. Only 183.5 feet of the uppermost part of the Lombard Limestone are exposed at this locality. The amount of actual stratigraphic separation represented by the medial covered interval is unknown, although the hummocky nature of this interval suggests that some recent gravity-induced movement has occurred. The absence of corals and the dissimilarity in bedding habit of unit 6 with respect to unit 4 suggests that the lower cliff sequence is not a down-dropped, repeatedexposure of the upper cliff sequence caused by slumping. The upper cliffs are believed to be autochthonous with respect to the Mississippian through Jurassic units exposed to the northon the north limb of a large, west-plunging anticline; the lower cliffs are believed to be allochthonous with respect to this block. The origin of the Lombard beds exposed in the lower cliffs probably lies just to the east,as transport, via slumping, has been to the west. Westward gravity sliding on non-parallel, intra-Lombard planes of failuremay have juxtaposed the two cliff sequences to within 21 stratigraphically vertical feet of each ôthr. Th ôrinii.1 tratigraphic separation of these beds, or 402 their lateral equivalents, was probably greater than thepresent 21 feet, so some unknown amount of Lombard sectionprobably is iiissing. The presence of a post-Jurassic, pre-Quaternary colluvium fault less than 0.9 mile east of the easternmost cliff exposures, and the Recent age of the latest slumping episode which created the cliffy exposures (suggested by the hummocky, cracked ground of the the covered interval) indicate that westward transport was minimal. The Chesterian coral age of the lower cliff sequence, and the conformable(?)or disconformable(?) occurrence of themsden at the top of the upper cliff sequence supports a Lombard Limestone classification for these rocks. It seems unlikely, in addition, that the intra-Lombard planes of failure cross-cut bedding at high enough angles to juxtapose two Lombardsequences of initially great vertical separation, given less thanone mile to translate. The true separation, obscured by the covered interval, is, therefore, believed to be minimal and this measured section is considereda valid representation of the upper part of the Lombard in the north-central Gravelly Range. This location can be reached by driving south from Ennis, Montana, along US 287 to the fish hatchery/Varney recreational area turnoff. Turn west off of the highway, cross the Varney bridge, drive approximately 0.4 mile toa left-hand turnoff, and continue due south. approximately 0.7 miles south of the Kent Ranch, turn west toward the Gerard Ranch. Just before this ranch, turn south onto Forest Route 292. Continue south-southwest to the crest of the Gravelly Range. t the junction with Forest Route 290, turn south. The Clover Meadows area is located approximately two miles southeast of the junction of FR 290 and FR 163 (Warm Springs Road). Hike approximately 0.4 mile west of FR 290 to the cliff exposures. 403 Unit Litholopy Ft. 11 DOLOMITE: White (N9); saccharoidal (moderately crystalline); thick to very thick beds; massive; laterally discontinuous ledge-former; moderately well exposed; basal C?) msden Format LAflM. 10 FOSSILIFEROUS MUDSTONE: Very light olive (5 V 7/1), weathers to light gray CN8) to white (N9); microcrystalline; thin, planar to slightly undulatory beds with parallel, slightly undulatory, laminated splitting habit; few echinoid ossicles, broken pelecypods, ostracodes; fossi is randomly oriented and distributed; small, ovoid, white clay-filled pockets common; no petroliferous odor; slope-former; poorly exposed; upper and lower contact obscurred; thin ledge crops out one foot below, and is parallelto, unit illedge...... 9 FOSSILIFEROUS WACKESTONE: Very pale yellowish brown (10 YR 7/2), weathers to light gray to grayish blue (5 PB 5/2); microcrystalline; medium to thick beds with minor parallel, planar to undulatory, laminated to flaggy splitting habit; most beds lacking internal splitting habit; echinoid ossicles, disarticulated and (many) broken pelecypods, broken brachiopods, indeterminate coral fragments, ostracodes; much finely comminuted fossil debris; fossils randomly oriented and distributed; very weak petroliferous odor; ledge-former...... 46 8 DOLOMITIC MUDSTONE: Yellowish gray (5 V 7/2), weathers to yellowish gray (5 V 8/1) to light olive gray (5 V 6/1); microcrystalline to finely saccharoidal; silty; thick bed; non-fossiliferous; scattered, small black (carbonaceous5) wisps common; very weak petroliferous odor; basal contact covered; thin bed with parallel, undulatory, fissile to laminated habit overlies thick bed with sharp, slightly undulatory contact; sharp, undulatory contact between thin bed and unit 9...... 7 FOSSILIFEROUS MUDSTONE: Moderate yellowish brown (1.0 YR 3/4), weathers to pale grayish orange (10 YR 8/4) to pale grayish blue 404 (5 PB 612); microcrystalline; dolomitic; thin to medium, planar beds with minor parallel, planar to slightly undulatory, flaggy splitting habit; echinoid ossicles, disarticulated and broken brachiopods and pelecypods, trilobite fragments, ostracodes; fossils randomly oriented and distributed, but weak shape fabric locally; very subdued ledge-former to slope-former; poorly exposed...... 22 6 FOSSILIFEROUS WACKESTONE: Pale yellowish brown (10 YR 6/2), weathers to moderate yellowish brown (10 YR 5/4) to pale red (10 R 6/2); microcrystalline; medium to thick, planar beds with local, minor, parallel, planar to slightly undulatory, slabby to blocky splitting habit; disarticulated and broken brachiopods (including indeterminate Product ids), echinoid ossicles (including Pentacrinus) and partial stems, fenestrate and indeterminate ramose bryozoan fragments, disarticulated trilobites, ostracodes; fossils randomly oriented and distributed, stand with slight relief on weathered surface; small, local manganese dendrites on weathered surface; horizontal burrows; weak to moderate petroliferous odor; ledge-former...... a 12 5 COVER: Grassy; hummocky; moderate brown (5 YR 4/4) to moderate reddish brown (10 YR 4/6) soil; scarce fossiliferous wackestone float...... 21 4 FOSSILIFEROUS WCKESTONE: Dark yellowish brown (10 YR 4/2), weathers to pale yellowish brown (10 YR 5/4) to grayish orange (10 YR 7/4); microcrystalline; thick to very thick beds, with locally pronounced parallel, planar to slightly undulatory, slabby to blocky splitting habit; many echinoid ossicles and fragments, disarticulated and broken brachiopods, fenestrate and indeterminate ramose bryozoan fragments, corals (including Siphonohvllia sp.), partial trilobite molds, ostracodes; fossils randomly oriented and distributed, stand with slight to moderate reliefon weathered surface; corals chiefly occur in upper 10' of unit, most randomly distributed, few clustered; few chert 405 nodules and stringers; strong to very strong petroliferous odor; cliff-former...... 24 3 SPPRSELY FOSS ILIFERDUS WflCKE9TDNE Dark yellowish brown (t YR 4/2), weathers to yellowish gray (3 V 7/2); microcrystalline; thick, planar beds with parallel, undulatory, laminated to flaggy splitting habit; echinoid ossicles, disarticulated and broken brachiopods, fenestrate fronds and indeterminate bryozoan fragments, ostracodes; fossils randomly oriented and distributed; many horizontal burrows; moderate petroliferous odor; sharp, slightly undulatory upper and lower contactswithunits4and2 ...... 3 2 FOSSILIFEROUS PACKSTONE: Very light olive gray (5 V 7/1), weathers to light gray (N7); microcrystalline; medium to thick, planar beds with absent to minor parallel, planar to slightly undulatory, flaggy to slabby splittng habit; few, very thin to thin interbeds with parallel, planar to undulatory, laminated to locally fissile splitting habit; echinoid ossicles (including Pentacrinus) and fragments, few whole and many disarticulated and broken brachiopods, corals (including Siphonophyllia ep.), gastropods, indeterminate bryozoan fragments; most fossils parallel to bedding, randomly distributed, stand with slight relief of weathered surface; corals concentrated within 2' interval (18' to 20' up section), scarce throughout remainder of unit; horizontal burrows; many chert nodules (up to 8" diameter) and stringers (up to 25' long and 4"-!" in diameter); weak petrol iferous odor; cliff-former...... 23 COVER: Fossiliferous wackestone and packstone float (some with corals, including Amplexizaphrentis large sp.); many very large talus blocks; light gray (N7) tovery light gray (NB); talus field at base of cliffs ..... unk. TOTAL: 183.5 feet 406 IX. SHEEP CREEK CANYON SECTION North side of Sheep Creek Canyon, N 1/2, NE 1/4, NW 1/4, section 18, T. 9 S., R. 8 W., GallagherMountain quadrangle, U.S.G.S. 7.5 minute series. Kibbey Formation section measured from west to east, beginning at uppermost limestone ledge of Mission Canyon cliffsequence. The section is measured along a N 40 E traverse, approximately 400 feetnorth-northwest of the dirt road along Sheep Creek. The Kibbey is very poorly exposed here as isolated, vertical,very low relief outcrops separated by soil-covered intervals of variable thickness. This location can be reached by travelling approximately 8.3 miles south from Dillon along BlacktailDeer Creek Road to the Matador Cattle Ranch (section 32, T. OS., R. 8W.;Reck Island Ranch on county map). Continue approximately 1.8 miles to a dirt road which turns northwest toward the BlacktailMountains. Follow this road to the fenceline and gate at themouth of Sheep Creek Canyon; park here. Hike west along the dirt road for approximately one-quarter mile. At this point the canyon abruptly widens, coincident with the MissionCanyon-Kibbey contact. The Kibbey is represented by the gently sloping section between the Mission Canyon cliffs to theeast and the moderate to steep slopes, underlain by the LombardLimestone, to the immediate west. The land west of the fenceline along the east entrance of the canyon is privately owned, butpermission to enter this area can be obtained bywriting to Don Connover (do Connover Ranch, Dillon, Montana). 407 Unit Ljtholopy ft. 15 SPARSELY FOSSILIFEROUS WACKESTONE: Dark yellowish brown (10 YR 4/2), weathers to pale grayish orange (10 YR 8/4) to medium light gray (N6); microcrystalline; thin- to medium-bedded; echinoid ossicles, disart iculated brachiopods, ostracodes(?); fossils randomly oriented and distributed; weak petroliferous odor; ledge-former; base of Lombard Limestone...... unm. 14 COVER: Grayish orange (10 YR 7/4) to moderate yellowish brown (10 YR 5/4) soil and scarce limy siltstone to fine-grained sandstone float...... 25 13 QUARTZ ARENITE: Moderate yellowish brown (10 YR 5/4), weathers to very pale yellowish brown (10 YR 7/2); very thin, slightly undulatory laminations of medium sand and very fine sand; subrouncled to rounded quartz grains; very thin, slightly undulatory beds; calcareous cement; non-fossiliferous; very subdued 1 edge-former...... 1. 5 12 COVER: Grayish orange (10 YR 7/4) to moderate yellowish brown (10 YR 5/4) soil; scattered, scarce, silty to sandy dolostone and quartz arenite float...... 17 11 QUARTZ ARENITE: Dark yellowish orange (10 YR 6/6), weathers to grayish orange (10 YR 7/4); fine-grained; subangular to subrounded quartz grains; no discernable bedding; massive; mottled; dolomite- cemented; non-fossiliferous; slightly friable; very subdued ledge-former ...... 5 10 COVER: Moderate yellowish brown (10 YR 5/4) soil ...... 4 9 DOLOMITIC QUARTZ ARENITE: Pale reddish brown (10 R 5/4), weathers to pale red (10 R 6/2); fine-grained; subangular to subrounded quartz grains; mottled; burrows and root tracesi?); dolomitic; non-fossiliferous; friable; very subduai ledge-former ...... 2 8 COVER: Grayish orange (10 YR 714) to pale yellowish orange (10 YR 7/2) soil; isolated dolomitic(?) to moderately limy, very fine-grained quartz sandstone and siltstone float...... 39 7 SANDY DOLOSTONE: Pale yellowish brown (10 YR 6/2), weathers to very pale orange (10 YR 8/2); very finely crystalline; scarce subrounded, very fine-grained quartz grains; extensivey mottled; many clay scallops and wisps; non-fossiliferous; dense; very subdued ledge-former ...... 2 6 COVER: Dark yellowish orange (10 YR 6/6) soil ...... 10.5 5 SILTY DOLOSTONE: Dark yellowish orange (10 YR 6/6), weathers to grayish orange (10 YR 7/4); very finely crystalline; slightly silty; mottled/patchy; dense; non-fossiliferous; very subdued ledge-former...... 2 4 COVER: Dark yellowish orange (10 YR 6/6) soil...... 4 3 SILTY DOLOSTONE: Dark yellowish orange (10 YR 6/6), weathers to pale grayish orange (10 YR 8/4); very finely crystalline; slightly silty; mottled; dense; non-fossiliferous; very subdued ledge-former ...... 1 2 COVER: Moderate yellowish brown (10 YR 514) soil ...... 5 MUDSTONE: Medium gray (N5), weathers o light gray (N7); finely crystalline limestone; slightly brecciated; cliff- and ledge-former; top of Mission Canyon Limestone; uppermost ledge is discontinuous, with Kibbey soil filling gaps along strike (= undulatory contact? on Mission Canyon Limestone) ...... unm. TOTAL: 118.5 feet 409 APPENDIX B: SOURCES FOR KIBBEY FORMATION AND LOMBARD LIMESTONE ISOPACH DATA Sect ion Source 1. Snowslide Mountain Witkind, 1964 2. Red Rock Lakes area Witkind, 1976 3. Red Rock River This report 4. Clover Divide This report 3. Sawtooth Mountain This report 6. Sunset Peak This report 7. Hogback Mountain This report 8. Sliderock Mountain This report 9. Snowcrest Mountain This report 10. Clover Meadows This report 11. Horse Prairie area U. J. Soodhue,in prep., communicat ion, 1983 12. Armstead ant icline area Hildreth, 1980 13. Sheep Creek Canyon This report 14. Baldy Mountain Had icy et a 1.,1980 15. Station 166 (Gravelly Range) Hadley et al.,1980 16. Station 170 (Gravelly Range) Hadley et al.,1980 17. Wigwam Creek (Gravelly Range) Had icy et al.,1980 18. Greenhorn Mountain area Sharp, 1969 19. Big Dry Creek Tysdal, 1970 20. Locality 1 Brewster, 1984 21. Locality 2 Brewster, 1984 22. Locality 3 Brewster, 1984 23. Locality 4 Brewster, 1984 24. Locality 5 Brewster, 1984 25. Middle Fork Sixteenmile Canyon Guthrie, 1984 26. Horse Mountain Guthrie, 1984 27. North Angler Lake Guthrie, 1984 28. Bighorn Lake Guthrie, 1984 29. Southeast Sacajawea Guthrie, 1984 30. Ross Peak Guthrie, 1984 31. Maynard Creek Guthrie, 1984 32. Bridger Peak Guthrie, 1984 33. Bridger Canyon Guthrie, 1984 34. Rocky Canyon Guthrie, 1984 35. Elkhorn Mountains Kiepper et al., 1957 36. Lombard Station Wardlaw and Pecora,1985 37. Bell Canyon Ward law and Pecora,1985 38. Railroad Canyon Wardlaw and Pecora,1985 39. Townsend Harris, 1972 40. Jefferson Canyon Harris, 1972 41. Logan Harris, 1972 42. lost on Harris, 1972 43. Pshbough Canyon Pecora, 1981 410 APPENDIX C COLLECTION LOCATIONS OF SURFACE SAMPLES FOR GEOCHEMICAL ANALYSES (PETROLEUM SOURCE ROCK POTENTIAL) Map Section Map Sample Lombard Ls. location name Coordinates number lithofacie_ I Red Rock SW 1/4, NW 1/4, 1 Lime mudst. River section 28, 2 Lime mudst. T. 13 S.,R. 7 W. 3 Lime mudst 4 Lime mudst. II Clover NW 1/4, SE 1/4, 5 Lime mudst. Divide and 6 Lime mudst. SE 1/4, NW 1/4, 7 Lime mudst. section 23, 8 Lime mudst. T.12 S., R. 6 W. 9 Lime mudst. 10 Lime mudst. III Sawtooth NW1/4, SE 1/4, 11 Caic..shale Mountain section 8, T.12 S.R. 5 W. IV Sunset NW1/4, SE 1/4, 12 Fossilif. Peak section 24, wacke-pack. T. 11 S., R. 5 W. V Hogback SE1/4, section 6, 13 Limemudst. Mountain T.11 S.,R. 4 W. 14 Limemudst. 15 Caic.shale 16 Calc.shale VI Sliderock SW1/4, NW 1/4, 17 Limemudst. Mountain I section 24 18 Limemudst. T. 10 S., R.4 W. 19 Limemudst. VII Snowcrest SE1/4, NE 1/4, 20 Limemudst. Mountain section 1, 21 Limemudst. and 22 Limeraudst. SW1/4, NW 1/4, section 6, T.10 S.,R. 3 W. NOTE: 1) Roman numerals under map location heading correspond to Figure 54. 2) Sample numbers correspond to those on tables 3 and 4. 411 APPENDIX D GAS CHROMATOGRAPHY RESULTS Twenty-two Lombard Limestone surface samplescollected in the Snoworest Range were analyzed for petroleum sourcerock the six potential. Gas chromatography analyses were completed on samples which yielded the most promisingpotential source rock values; these chromatograms are arranged bysample number, as listed below (see Appendix C for Township andRange coordinates of sample locations). Sample Lithofacies Collection site Lime mudstone CloverDivide 11 Calcareous shale SawtoothMountain 12 Fossil. wacke-pack. SunsetPeak 14 Lime mudstorie HogbackMountain 15 Calcareous shale HogbackMountain 16 Calcareous shale HogbackMountain Sample 10 / Lime mudstone / Clover Divide 80. 4 INJECTED 1/100 a 88.80 62.74 C- '-IC Iii 2 a 38.88 0a aLi I 26.02 '-4 -J \jJLJ1Ji U. 17 0.00 8.85 13.70 20.55 27.40 94.28 41.11 47.88 64.81 AT in minutes SAMPLE: DJB MONTANA INJECTED AT 18: 25: 31 ON FEB 13.1985 P4eth: HMWOO Raw: RT9864 Proc: PR7 I-. N) Sample 11 / Calcareous shale / Sawtooth Mountain 180.23 INJECTED 1/300 a U, 153.28 I.. 0) 118.29 C- ID Ui I a 79.32 a aUi I- 42.35 -I _JIAJ.$1u1 5.38 0.00 8.85 13.70 20.55 21.40 34.28 41.11 47.98 54.81 RI in minutes SAMPLE: DJB MONTANA INJECTED AT ii: 17: 32 ON FEB 13.1985 t4eth:HP4WO9 Raw: 1119662 Proc: PHI I-. (A) Sample 12 / Fossiliferous wackestone-packstone / Sunset Peak 87.81- INJECTED 1/300 a a 58.51 IC) a) 45.40 ID LU a 34.30 a aLU :3 I- 23.19 0-J L 12.08 0.00 8.85 13.70 20.55 27.40 34.28 41.11 47.98 54.81 HI in minutes SAMPLE: OJB MONTANA INJECTED AT 12: 28: 49 ON FEB 13.1985 Raw: RT9668 Proc: P112 Meth: HMWO9 I-. .I. 102.30 Sample 14 / Lime mudstone / Hogback mountain 1/100 a(.3 83.83 IDC-a) 85.38 Uiaw 48.88 I-.I-0-Ja 28.41 RI in minutes8.94 0.00 -[INJECTEDMeth:SAMPLE: HMWO9 038 MONTANA __UJLJJiL8.85 13.70 Raw: RT9665INJECTED AT 17: 14: 08 ON FEB 13. 20.55 27.41 Proc: PR6 34.26 41.11 1985 47.87 54.82 Sample 15 / Calcareous shale / Hogback Mountain toe. 88 INJECTED 1/300 0 83.88 a) 85.40 a) C- 40 71a LU 1 a 4. 82 0a aLU :3 I- 28.44 I-s -j x0 8.88 HT 0.00 8.85 13.70 20.55 27.41 34.28 4i.11 47.87 64.82 RI in minutes SAMPLE: DJB MONTANA INJECTED AT 14: 51: 26 ON FEB 13.1965 Math: HMWO9 Raw: 1119668 Proc: PR4 U Sample 16 / Calcareoue ehale / Hogback Mountain 120.07 a 97.67 L 7588 C- go Ui a 53.48 a 31.29 909 0.00 8.85 13.70 20.55 27.40 34.28 41.11 47.96 54.81 AT in minutes SAMPLE: DJB MONTANA INJECTED AT 13: 40: 07 ON FEB 13.1985 I4eth: HMWO9 Raw: R19667 Proc: PR3